Here's a tutorial on how I make my skins for The Sims 3. The process works for The Sims 4, too. I personally don't play it, but I've made skins for both games when I have in the past :)
Results from this video, pinned on my blog!
https://simske.tumblr.com/
What you'll need:
S3PE- Extracting Skin
TS3Ripper (Optional)
Photoshop
Blender
