A problem that I run into my game is that my CAS sims often in up looking similar. This isn't intentional, it's just something I notice once the sims are out and about in the neighborhood. I've remedied the problem by diversifying the skins and eyes I use, but what do you do to make sure each of your CAS families are unique?

Make your own faces instead of using the templates (it might also help if you use bodyshop since there's more options there), or maybe make a few sims in CAS, roll the pacifier, delete the parents (while in CAS) and then do that again until you get a face you like? (also worth noting, a lot of sims in the sim bin have unique faces, though some don't mix too well with each other).

I like to mix face 26 (? with the elf ears and really nice shaped eyes) with face 2 and I think 5? (I don't remember). Makes for really interesting (or possibly weird) looking sims depending on which parts of which face template I mix.

Make note of the templates you're preferring, and avoid them. Push a slider a leeeeetle bit further than you think is attractive. Randomize all elements of appearance.

Let go of your preconceived notions about "attractiveness" and how people "should" look, and it's easy. You don't have to go to the extremes I do to get the job done.

I added non default templates to CAS to give my game a wider range of face templates to choose from. I then make new sims by randomizing and changing the individual features. I do tend to go for 3 noses as most of them are crazy, but starting from different bases gives me more variety even if my noses are often the same three with tweaks.
Also having a good choice of cc with eyes, skin, hair and other things like piercings, glasses, tats, moles, freckles and wrinkles all help.

Lately I've picked a nationality for my Sim, and gone for characteristics that are common in that area of our world. For example, I made an elder female Sim that was supposed to be the equivalent of an older chinese woman. I am quite happy with how she came out, and she's definitely not the same as most of my Sims, who are more your typical west world idea of pretty female.

Doing Sims with a goal in mind has made me more comfortable with user sliders, and that has lead to some more variety.

Pretty much this. I love the look of the Strangetown sims (Nervous Subject excepted ). I would add playing with genetics. Either the genetics from the premades or from two sims you made in CAS. Then have CAS create some offspring and see if you get something you like. I have found that the new generation of Strangetown has a lot of good-looking sims, but with some interesting aspect to them, like a nose that is a little big, or their cheeks are a little too round and puffy... That way they are unique but not necessarily a frustration to find a good hairstyle for.

Some examples:

If you're making CAS sims build them in body shop, look at your other saved sims and make your new sim look different. I have 42 regular non-default face templates, a set of default replacements, and another four with various forms of elf ears, that in my opinion look nicer than the face 26 ears - when creating sims I make an effort to use every one of the 68 regular templates in my game and if they still look too similar I throw in the four fantasy templates. I also have 80 different genetised non-default skins of which only ten are fantasy colours, the rest are various styles of maxis match, and I lost count of how many genetised eyes at 150 so my sims tend to look different anyway.

I find if I'm not trying to make them all look attractive or odd but rather have them all look fairly averagely attractive then they have more unique features and continue to breed their unique features through the hood rather than one set of features dominating on every sim by fifth gen.

I've said this before but I think it's worth saying again: one thing I did when I used to post on usenet with a group of people there was swap sims between us. There are several sims in Little Carping who were originally made by other people. It's a really excellent way to get different looking sims in your game because they are not made by you. I know there are a lot of sims for download on sites like this but what I liked about that in particular was that we posted just our 'every day sims' - sims we'd been playing or liked for some reason. Not the sort of 'best effort' sim you might get people uploading to a site like this. One thing we might like is a sim exchange for the regulars on this board. I certainly could contribute and would probably like to download other people's sims.

I roll a D20 and use the number on that. So first I count along the templates from the one which is already selected and use that template. Then I roll again and count through the sliders, so 1 and 2 refer to the first slider, 3 and 4 to the second slider, with the odd number meaning "pull to the left" and the even meaning "pull to the right". I'll pull it around until it looks different, interesting, nice or odd, and then roll again. I sometimes use the individual template elements for the different face parts but if it distorts the face too much then I hit undo and just go for the sliders.

Once I'm done with the random selecting of sliders to pull around I'll look at the entire face, see what kind of feel I get from it (especially combined with skintone and hair colour) and then go and tweak any parts I don't like.

Some pics below. I feel like I can tell a lot about a sim's personality by looking at their face and often in CAS I'll adjust their personality to match or sometimes I use the personality to inspire the feeling of the facial characteristics.

Personally I like swapping out my default replacement faces every once in a while to add some diversity across neighborhoods, and if I create any sims in CAS I further edit them so they don't look like the townies. As some people have already mentioned above, non-default replacement faces are a godsend, too.

Another thing I like to do is download some premade sims and create some of my own in Bodyshop, then CAS-spawn their children. After that I delete the original sims in CAS, age the children up to adults (or whatever age I want them to be), and then make some changes here and there. If you want them to be further diversified, you can take one step further and make CAS-spawns of the CAS-spawns xD Makeup also goes a long way, especially if you have the kind that adds special effects (dimples, freckles, eyebags, highlighting/shadowing certain facial features, etc).

I think, if you use default replacement face, the problem is there, because default replacement tend to be based on a idea of beauty instead of the Maxis exaggeration of features of every race and ethnicity.
I decided to remove facial default replacement, and now is easier to do unique sims. Even when you aim to make all of them beautiful.

Skin and eyes replacement are fine. Sims look better.

I will sometimes roll for which face template, mouth, nose etc to use. Then I look at what I end up with, try to fiddle with sliders to make them fit together, and if one facial feature just does not work with the rest, I may re-roll it. (I get to re-roll one or at most two, and I can't re-roll them over and over. Make it work.) Other times I will make a list of characteristics - wide nose, hooked nose, small nose, round cheeks, narrow cheeks, big eyes, small eyes, tilted eyes, pouty lips, narrow lips, etc - and randomly roll for a few of them, then create a face with those characteristics. It's especially fun when you roll things like eyes tilted in one direction and eyebrows tilted in the other, or a wide thin mouth and narrow cheeks...

And then sometimes, I will create two sims as described above, then randomize a child of theirs. That can produce some very interesting results, and you can get recessive genetics from scratch so the next generation might show more variety in coloring.

Great topic

What I have started doing is trying to make sims based on real people (celebs mainly, not people I know) and though they are not uploadable as celeb sims, they are different enough to give my hood some variation.

Making them based on real people works too. Often I'll create a person I know in RL or a celebrity and then save them in Body shop. Then use that as a template to create CAS sims in game which I then either gender switch, age up/down or I'll merge two of them to create children. I like to create families who are genetically alike so I always use the "make a baby" function in CAS too.

I wanted some interesting genetics for my most recent hood. I googled "ugly man" and tried to recreate the picture I liked the best. I'm pretty happy with the results. :D

I would suggest Body Shop, but when I tried that it ended up terribly. While BS has more options on what you can do, the lighting is terrible and, when used in CAS in-game, it looks vastly different from what I had in BS...

C-A

I often choose one or two parts of the face that should stand out. For example a big witch nose, small rotated eyes or a big jaw. I make these first and then start editting the other parts of the face, without altering the sliders I used for the outstanding parts. I always find myself editting the face in a entirely different way than normal, because the normal idea of beautiful looks fugly with these outstanding parts of the face. Most of the time the result is beautiful, unique sims.

Like a few of the other posters, I tend to play the premade Sims (even the ones that are not considered "attractive" by many). Also, to mix things up a bit, I usually create at least five unique looking Sims to add to the neighborhood as well. I also have a mix of default face templates - fleshing out the in-game ones that I just really don't like.

And I agree wholeheartedly with those that suggested playing around in bodyshop. Getting out of your comfort zone when creating a Sim, really does give you the opportunity to add more variety to their appearance.

I tend to base my sims off of real people's faces. Sometimes that doesn't work with a gender switch though so their children can look a bit funny. Sometimes they end up coming out nothing like the celebrity they are supposed to be but come out different to my other sims regardless.

Here's one of my families.

CatMuto, if you're going to make a lot of sims in bodyshop, it's worthwhile to find mods that make the interface easier to work in. There's mods for lighting and I believe for changing the resolution you're working at. Ask in WCIF if a search in the downloads section doesn't help you.

Please link us to them! I've been looking for non default templates, and they're hard to find!

The lighting in Bodyshop is bad. I usually give up and end up using CAS.

I'm not very good at this, mainly because I tend to make Sims that are attractive to me, rather than aiming on making them really unique. I usually start off with whatever face template CAS/Body Shop has generated, but then modify it with the sliders (and sometimes face parts from other faces) until I get a face that is pleasing to me. Using random templates, and them modifying them with the sliders ought to produce unique Sims, and I suppose that technically they are all unique, but the way I use the sliders probably actually reduces their uniqueness. For example I nearly always turn up the corners of their mouths just a little, because I don't want to look at grumpy faces. I think when I'm in CAS or Body Shop, I can't resist the temptation to create someone who (a) is believable, and (b) I would instinctively like if I met them.

In real life I tend to recognise people more by their hairstyles and clothes than by their facial features. People who change their clothes and hairstyles frequently can therefore confuse me. But at least it's easier in The Sims, because they don't do this autonomously: some of my Sims are in fact always changing their outfits, but always into something I've chosen for them.

I recognise sims more by their hairstyles too. I had two sims who had the same hairstyle once and I kept mistaking them for each other (not that I do that with every sim that shares a hairstyle, but their faces were similar too). XD