There is very little sex, if any. This is a crucial difference between adult and young adult novels. Teenagers are interested in sex, of course, and sexual tension is fine. However, there can be absolutely no bedroom scenes. Keep your chapters between six and seven pages.
Kids have short attention spans.
An interesting voice and humor will hold a young adult's attention. Economy of words is extremely important. Keep your writing tight, focused, and sparkling. In a 90,000-word novel, there's a little room to ramble. Rambling in a young adult novel will make the reader stop reading.