I have seen teams use things like a hand clap, or sticking a hand out to signal you want the ball. I would encourage the latter to give a clear target, but with younger players a very good way is to have them learn to call the passers name, when they extend the hand. On the higher levels of the game, this isn't as effective because experienced players will use the sound to alert them to a pass coming. Professional players use a lot more discreet eye contact, or situational position to determine when a pass will be thrown. I'll give you one drill here which I also picked up from a Rumanian coach which some young players I worked with loved.
Tennis is just what the name describes.
That is the net. If a ball bounces more than once, or out of the reach of a player on the opposite of the net then the server leads 15-love. They player until a game is one and the serve is switched. You might have them serve and play with right handed push passes only, then maybe switch to left hand hook passes. Now I wouldn't recommend this type of drill to the high competitive level high school and college teams, but for youth teams they'll love it.