especially if you're early, ask permission to come aboard, and listen if they say 'no'. if they say 'yes', pick a spot. if where the sun is matters to you, think about that when picking (i try to stay out of the sun, but i'm a redhead and burn at the thought of the word 'sun'). boats and areas do things differently, but if there are tanks already at your spot, go ahead and set up for the first dive - put your bc and reg on a tank. *be careful if there are bungees!* unbungee, put your stuff on the tank, check with the pressure on, turn the pressure back off, and re-bungee. yes, at some point sometime, you'll try to get up with your tank still bungeed to the boat. we all have.
ask about how long once the boat is underway before you get where you're going. offshore nc, it's about 2 1/2 hours. off of the lauderdale area, about 20 min, so things differ. if you have quite a bit of time, organize and stow the rest of your gear under the bench or wherever they show you, and hang out with the other divers. be aware on long rides that lots of folks have taken dramamine or benadryl and may nap going out. chat with whoever is awake.
there will be a call to get dressed. leave your dry stuff in the dry area - keys, phone, wallet, clothes, etc. go put on your suit and booties, unbungee your tank and turn it on, put on your bc and snug it up, take your breaths while watching your gauge, spit in and put on your mask, all while at your spot. when they announce the pool is open, check that your buddy is ready and shuffle to the exit with your fins. either you or the mate will put your fins on. they may have a protocol to give them a number or another method to check off who is leaving the boat. they should tell you that in the briefing. hold your reg and mask, and weight belt if applicable, and hop grandly off! when you bob up, give a big 'ok' by tapping your own head, then go to wherever you and your buddy (or guide) were going to meet, whether at a line or at 20 ft or whatever y'all decided.
have a great dive. check your gas often.
coming up and going down, if the crew says to follow the anchor line down and up, then you follow the anchor line down and up. there are places that have different layers of current and you might can see the boat but a free ascent still might not be a good idea. do what you're told if at all possible. ditto how they tell you to handle their ladder - fins off and over your wrists, a fins-on ladder, handing fins up to a crewmember - all these are possible ways to handle it. if it's 'sporty' (unlikely off the panhandle), watch what the ladder is doing and time your upward scamper to take best advantage of how it is moving, sorta like riding a bronco.
change tanks. have a snack. keep your area neat and things out of folks' way. if someone sets a tank on your mask that was in the tank well instead of stowed, not their fault.
do it all again! it's a lot of fun.
larry says 'show up, look at the boat, look at the waves, go find a good cave instructor', but he's grumpy this morning.