I've added this bit too:
- As Pablo said, these are a minor part of a TJ's job.
- Only give them if: a) The referee wants you to. and b) The referee is looking at you.
- Don't wave arms around like a scare-crow, small and discrete gestures are more appropriate.
- Often the best way to show a penalty is to place your right arm across you, hand on the left shoulder (as if you were going to give it to the team on your left) - the referee should mirror. Agree before the match though. Then signal the offence.
- Remember your the TJ, not the referee! Don't overstep the mark.
- Make sure you're not peering over the referee's shoulder! try to compliment it, not to copy it!
- Watch players/ball carriers not the ball. Leave the ball primarily to the ref. You can watch for off the ball incidents he might not see.
- Body language is as important as when you referee. Get this right and they'll accept your part of a team of three, not just another TJ.
- Remember your priorities! Don't fart around giving tertiary signals because someone's bleeding and forget your running touch!