The blackout rule was created to give the incentive to go to games (which generates much more revenue per person than TV viewing). The problem is that its a false incentive because most people who were going to go to the game will do so anyway, and most people who don't want to will just hope that the games are sold out. Very few fans pay close enough attention and have a flexible enough schedule to wait until the last minute to find out if a game will be blacked out or not and buy single game tickets if it is.
Some things the NFL should do:
1. Make all teams allow ticket scalping. I know the idea of home games becoming road games sucks, but from the NFLs standpoint this will increase profits as more people will buy singles looking to make a profit on outsiders. This doesn't hurt the NFL at all, and frankly if teams can't handle visiting fans then they probably don't deserve to win anyway.
2. If they aren't selling out games, that means tickets are too costly plain and simple. If supply is fixed and demand doesn't meet that supply then changing price is the logical conclusion.
3. Finally, if they can't accept whatever price they have to drop tickets to in order to sell out each game, then the only option left is to improve the product. Being at games provides plenty of things that watching on TV doesn't and vice versa. The NFL's marketing department simply has to find more ways to make being at games more appealing to the fans vs watching on TV. Whether that is giveaways and prizes, better halftime and pregame shows, or just improved stadiums is up to them to figure out.