What are the best tutorials for changing game behaviors (not making new art or animations, but chaning how sims interact or what effects an action has)?

[rb813]

I think I'm at the point where I'm ready to dive in an start really learning how to mod this game, but it seems like a lot of the tutorials are more focused on the visual side of things; meshes, animations, etc. I'm more interested in changing the way things work in the game. Can anyone recommend some good (beginner-friendly) tutorials for that side of things?