First of all get your hands on the NFHS Football Rule Book which is what high schools use in all states except Texas and Massachusetts. I recommend spending $25 for the ARS Rules Study
http://www.rules-study.com.
As for workout. A good part of every football game is running. A good cardiovascular routine using bicycles or aerobics. Personally, it is step aerobics during the winter and on to the bicycle for the summer. And, an anerobic workout with weights primarily building lower body strength. My workout for most of the year is leg extensions, leg curls and leg presses. Then about a month before the season I lower the weight and focus more one strengthening the muscles for running.
Good luck!