Keep it simple starting out, Danny. Nickle/Dime vs passing sets (005, 104, 014), Normal vs the rest. Maybe a rule when to go for it on 4th down, a Pass Key for 005 and 014, maybe a prevent defense rule. That should get you started in the right direction and beating casual owners.
Greyghost had it right when he said get the player weights correct. Can't build a good team with the wrong parts.
Pernbronze started to get into the offensive and defensive playbook, which is
crucial because some plays work and some just don't in MFN.
It can be daunting, but you really, really need to take some time and search the forum for "rules", "player weights", and "gameplan". Sethrick has a ton of great advice on all three to help get you started (and give you an advantage over probably, 80% of owners). You will have to make time to do this, but it's so worth it.
Myself, I use less than a dozen rules, but I really work on the offensive and defensive gameplans: when and where to use runs, short, medium, long passes, down and distance, and keeping my opponents from keying on any tendencies.
I use basic rules and a basic gameplan to get through the regular season, but I'll make specific rules and gameplans for each opponent once the playoffs start.