I'd like to see a big change to the throw-in rule:
1) opposition players must be 5 yards away
2) ball can be put into play however you like as long as it's touched by another player within 5 yards (underarm roll, short kick)
3) current rules apply for longer throws, but both feet on the ground actually enforced
4) throw must be taken from no further forward than where it went out
5) 8 seconds to release the ball once the throwing team has possession, with a 5 second count down by the ref, like for goalkeepers. Drying the ball or switching thrower must still be done within the 8 seconds.
6) Any infraction results in the throw being given to the other team
This would speed the game up, reduce the time wasting, and allow a team to more easily retain possession, which should be their right, if the other team put the ball out of play.