Here's a bit from my other leagues constitution:
Rule Changes
* Any vote taken by the league to change the rules requires a 75% vote to pass (12 out of 16).
* Any vote taken by the league to change the rules between Feb. 15th and Week 17 requires a 100% vote to take effect immediately.
* If a vote taken between Feb. 15th and Week 17 receives 75% or more but less than 100% it will take effect the following season.
* Abstentions will be considered "Yes" votes.
* All poll votes will be final 5 days after they begin.
* Any unforeseen rule situation not specifically covered in the constitution will be determined by the league commish.
Some of the dates and numbers would have to be tweaked for our league but we've had a ton of good input in that league and have made some nice tweaks each year.
The other component to consider is trades, we could have some guys appointed to approve trades, we could just have me approve and have some sort of appeals process if someone objects or some combination of both.
If you have any input on how you would like the league run post it here...