With a brand new team and no clue who could do what, I let the coaches plan preseason game 1 where I got destroyed. For game 2 I still had no rules in place but I selected my own plays on both sides of the ball. Games 3 and 4 were the same but with more play tweaking and some generic rules.
For the regular season I will have my full set of rules and plays which may or may not change based on performance. Actually it will likely change a lot in the beginning as I continue to find things out about my team.
Concerning rules, the basic framework is constant but I change which ones I use based on opponent. More often than not I tend to start slow before I hit my stride once teams establish their trends.
For future preseasons I will use everything already established as I will need to get my new players acclimated to "The General Way".