Definitely Eyebrows and Foundation.
My skin's always been pretty okay, few blemishes, so adding foundation makes me confused [emoji14] that and it gets in my massive, dry laugh lines and makes me look like I have cookie crumbs all over my face...
As for eyebrows, mine are naturally pretty weird (I guess it's called "curly eyebrows") so "following their natural shape" makes no sense to me. I have still not figured out a good way to shape them consistently.
As for eyeliner, you really gotta just practice forever and compare results etc. It really is like art, finding a good technique for your specific brush or open, and learning how to use the tool to shape what you want. I think eyeliner is super fun :3