Rules: don't go crazy until you know the game pretty well. The basics:
Offense:
Fourth down-when do you want to go for it?
2 minute drills-half and game.
Short yardage/goal line-optional.
Defense:
Empty backfield sets-nickel/dime/quarter with full pass key.
Short yardage/goal line.
Balance depends entirely on your team, but it's risky and gimmicky to start getting too far above 60% in either aspect. A generally balanced offense is always toughest to slow down.
Plays: some work and many don't: look at what the good teams are running.
