I love creating sims and I find it hard, sometimes. I don't use CC, but I try my best to make every sim different from the next.
I think the best advice I can give you is to play with ALL the sliders. Don't be too concerned with how they look from male to female or teen to adult. You really just have to experiment and don't be too picky about which sim premades you start with because, if you do it correctly, they should look nothing alike!
The features I like to play with the most are the jaw/chin area and the nose. These two areas of the face make the MOST difference from sim to sim, imho. Adjusting the width of the face, the size of the eyes and even sometimes using wacky makeup from supernatural can be similar to contouring.
So, really, you just have to be open to trying new things. Sometimes, I look up interesting faces that inspire me. You can see the pictures of my sims in my showcase thread in my signature, if you'd like to see. First page, second post, has links to each sim for quick and easy find.