It depends on how much detail you want to go into and how important you want each year's draft to be. There's no single best way to run a keeper league - some people are happy with one player kept per team; others prefer being able to keep as many players as you want within the bounds of a salary cap.
As Arlo said, the possibilities are endless. Two things come to mind right off the bat -
1. Don't do it this year - wait until next year and announce the change prior to the draft.
2. If you ARE NOT going to use a salary cap, IMO teams shouldn't carry over more than 3-4 players at the most because teams can end stockpiling top guys and the league could end up lopsided with a few owners dominating every year.
"I'm normally not a praying man, but if you're up there, please save me Superman."
- Homer J. Simpson
I agree you should do it at least a year in advance because you go into a draft differently in a keeper league. I am in a 10 team- 6 player keeper league and we do NOT do the auction draft style- which I am not a big fan of. This is our fifth year into it and I love it
how long do you guys allow people to keep players? as long as they want? or 2 years, 4 years, etc? then they would be cycled into the redraft pool.....reason would be to keep someone from having LT the rest of his career...