Well for a scrum half the most important thing is a good passing game and getting to the breakdown quick so your fitness will need to be up to scratch as well. I suggest you get a rugby ball and put it in a bucket of water for about 10 minutes, it'll get a bit heavy. With the ball, place it on the ground and pass it like you're clearing from a breakdown and try and hit a mark constantly. This will help you hit your target all the time and your arms muscles will develop as well. I never was a scrum half but I've had this passed on to me. Good luck
