DS has never been very picky about what his clothes look like, but he was, and still is, quite picky about how they feel. DD is not very picky about how clothes feel, but pickier about how they look.
For both of them, I mostly just let them pick out their own clothes, preferably the night before if they have school the next morning. And I just make sure that I'm fine with them wearing pretty much anything in their dresser. We do have certain rules (no "princess" dresses or tank tops at school, for example), and I try to get them to dress appropriate to the weather. I know your daughter is a lot younger than my kids, but it's not too early to have her start selecting her clothes the night before.
And as for buying clothes, that has been a lot of trial and error. DS decided he couldn't wear jeans, most shorts, or any other long pants this spring. I found shorts he would wear, and bought about 10 pairs. Boring, but he's happy (and therefore I am!)
DS also has very sensitive feet. He used to be able to wear only a few different kinds of socks, and this year stopped wearing them altogether. We now have a deal that when he plays Minecraft (his absolute favorite thing in the entire world), he will wear socks. I'm hoping that this will desensitize his feet so he can start wearing socks again.
