Hey Rick,
It may take a few dives to get some of the other requirements squared away.
First, the light bulbs are fragile. Keep the lighthead in a beer cushie at all times when its not in the water or you're actually rinsing it. Don't remove the beer cushie until you stand up to head to the stern. All sorts of weird crap can smack your lighthead at the last minute.
Second, always jump in the water with the head clipped off. Don't hold it in your hand unless you absolutely have to. You never know what you might have to deal with, and its a PITA if you have some other issues upon entry. Before you descend, click on the switch, check the head to ensure you have ignition, and then get your other stuff, scooter, deco bottles, etc. all squared away...then unclip the head LAST. It's a good idea to do bubble checks and an S-Drill, even though its redundant, because in the rush to gear up someone may have inadvertantly overlooked something.
Third, like the other guys said, its important to practice with the thing in the water. Its normal to keep it in your left hand. The rationale is that if you had to offer your primary reg to someone you don't want to blind them simultaneously. But in an overhead environment, when running the reel, etc., in reality you'll be switching it from hand to hand (unless you're scootering) to pull and glide or negotiate obstacles, etc. If you hold it in your right hand, wrap the cord around your right arm to prevent it from becoming an entanglement or snag hazard.
If you suddenly need both hands, esp in an overhead environment, don't flail around with it - its easy to break the bulb. Instead, drape the damned thing over your neck - its fast and effective, do what you need to with both hands, then redeploy it.
Finally, (and this is debatable so take it for what its worth) never turn the thing off until you're ready to get back onto the boat. You'll endure all sorts of whining from buddies when you clip off the lighthead during the ascent. But heres the deal: sometimes when you turn them off they don't immediately turn on again. And sometimes, even on the ascent, things have an annoying habit of going seriously wrong. Like current, getting swept away, etc. Guys have had serious problems and couldn't signal their buddies, 'cause they turned off their lights and couldn't get them back on fast enough to be effective when they needed to signal for an emergency. So leave it on until you're ready to exit the water. The thing will become your primary means of communication and you need to be able to communicate immediately when a sudden problem develops.
FWIW. YMMV.
