Keeper Rules

I've had a 12 team league for the last 7 years, next year we voted to have one keeper for our roster starting next season. What is the best approach for doing this? I've heard of having to keep the guy you drafted in whatever your drafted him and forfeiting that round draft pick the following year. And I've also heard that you just pick one player keep him as your first round pick and start the draft like regular. All ideas welcomed. Thanks