I have the misfortune to be a combination of a perfectionist and shakey hands so it'd be eaiser to list what I don't have trouble with. That's why the art on my comic is done by GigaNerd and TheMightyBox
Because not all problems can be solved by sleeping at an inn. Updates Saturdays.
Backgrounds. Even when I get them right, they seemed to have taken more work than they should have.
Composition. In line art, ending up with the same line density everywhere gives a flat, grey outlook, so the level of details and/or shade shouldn't be uniformous, but I get that so very wrong often.
Clothes. Not really drawing them, but designing them.
Crooked teeth. Can you draw a cute character with crooked teeth? When I try, the teeth either look normal, or completely freaky and the character isn't cute anymore. Same with other minor defects, like wrinkles and pimples. Either they're too subtle and readers don't realise that's what they're meant to be, or they're too blatant and the character looks like a butt.
I usually sit down and have my laptop ready to find reference images for anything, or a pile of pre printed references ready to go because I can pretty much not draw anything from memory, at all, except people...