Two things to do when visiting Tikal:

1.) Take the sunrise tour, whether you choose to stay overnight in Tikal or to come in from Flores. I only paid 100q and that included early entrance (not your actual ticket though) AND a three hour guided tour. You get to see the sunrise from atop the tallest temple- Temple IV. A very special experience.

2.) If you stay overnight in Tikal, get there in the early afternoon the day before. You can buy your ticket for the next day early (at like 3 or 4) and also use that ticket to enter that very afternoon. I did this and was bascially ALONE in Tikal, even in the main plaza. I climbed Temple V with no one around snapping photos and enjoyed the jungle and the views in reflective peace and quiet (jungle sounds excepted).