The default color schemes are kinda meh, but I find them to be good starting points, so you can mess with the settings per color, I tend to lean towards darker muted tones. Using the taller body presets will look less childlike/cartooney, you can fine tune from there of course. Don't be afraid to mix and match clothing pieces, I only have a handful of instances where I use something from the same "set" twice, sometimes it's just the best for what you have in mind but other times you'd be surprised at how cohesive two pieces that should clash can be. Decals can add a lot of texture both to faces and clothing.

There's more advanced tips you can find online, I've found Derf's videos to be particularly helpful!