If I should go into detail about my charaters appearance, after it gets into the major plot. I dont really know how, because her looks are what she is, her green eyes, black hair, etc. (story in signature)
Pull out a copy of a book you have there and see how the author handled the character's appearance. I just pulled out The Truth About Forever by Sarah Dessen, and she doesn't describe Macy until chapter 2: EDIT: Oops, I should have added that when Dessen describes the MC, it's always for a reason; it makes sense in terms of the story. So in the piece above, she's describing her as part of a narrative about how Macy didn't used to care about how she looked, but now she's concerned about looking perfect. The first few paragraphs in that chapter deal with that.
Something to consider is how the character feels about their appearance. For example, mine hates how his nose is a little pointy and but likes how he is just naturally lean