Time for outside input. Get into a YA fiction critique group, sign up for a critique with an author/editor/agent at a conference, or hire a freelance editor. Fresh, knowledgeable eyes can see what you’ve become blind to. In the meantime, work out the kinks item by item. Do a pass just for characters, making sure they grow through the story; a pass for plot, ensuring that all events build upon each other to move the plot forward; a pass for dialogue, checking the flow and the balance between talking and telling; a pass for setting, giving readers enough to picture the place and characters to act on or react to; and a pass for word choice, replacing dull words with dynamic ones.