The participants in your league -- they might be called owners, managers or coaches -- are the most critical factor in its success. You'll need at least eight and as many as 14 owners (an even number avoids bye weeks). You want owners who are likely to see the season through, not drop out in November.
The best rule is to pick people you know. If you include one jerk or hothead, it can spoil the fun for everybody. Watch out for pre-existing conflicts between potential owners. Remember, it's hard to get somebody out once you've gotten him or her in.
Make sure coaches are roughly equal in their expectations, their level of seriousness and their football savvy. Decide in advance whether this is going to be a casual league mostly for fun or a hardcore league for NFL junkies.
The owners you choose must know what fantasy football entails. They should understand the time commitment. And they should recognize that just knowing the NFL doesn't necessarily mean knowing the ins and outs of fantasy football.
Have several alternate owners in mind. Confirm participation a week ahead and be ready to recruit someone else if a perspective owner cancels.