Before the kickoff in high school games, I usually say something like "make sure your buckled up and have your mouthguard in" to both teams. To the receiving team I also add "don't block below the waist" or to the kicking team "wait for the whistle". What should I say when doing higher level games? It seems a bit childish to tell a collegiate player to make sure he has his mouthguard in, but maybe that is what needs to be said.

Raise your hand when you're ready to go, don't kick it until you hear the whistle from the referee. Good luck.

Use your judgement.
 

I think its good to have all the officials look at the players in their area and make sure required equipment is properly worn. Thats a good mechanic on your part. Over here at the end of a time-out I'll say "mouth pieces in, chin straps on".

Scrimmage kick formation I'll say: "watch the center".

I think its good if you say these things during the game because it 1. helps the players through preventive officiating and 2. it prepares you mentally for what you need to be doing during the game.

A thought...
 

I was on the chain crew at the Hula Bowl a few years ago. During a time-out the HL went up to the offensive linemen and was telling them to watch their hands. Seems like they were getting a bit too aggresive and grabbing shoulder pads, etc.

So what you are doing sounds great to me.