I tend toward the practical and a bit crude, so you've been warned.
1.) Plan to have your smart phone with GPS capability on the dive deck part of the time. If getting it dripped on bothers you, get a zip lock bag or similar. Before each dive, they may draw a dive site graphic and talk about it. Use the phone to take a photo. Even if you don't have cell service, your phone can take a photo with GPS coordinates included. I got an iPhone app. later off Apple's App. Store to get those. Some dive log software (e.g.: MacDive) lets you input GPS coordinates and displays them on a map. It's something you may someday wish you had.
2.) Toilets (a.k.a. marine heads) on boats often clog really easily. Unclogging them is a nasty job for a crew member. If you're a big guy who eats a lot, how can we have peace? Well, there's a (ridiculously small) little trash can in the bathroom. Use that rather than flush your toilet paper wads. I have no idea what other people do, and it's probably cruder than most people would mention, but hey, that's why you've got me!
3.) Between dives, head up to the top deck and lay in a lounge chair and doze. I've been blessed to rack up high dive counts (on live-aboards every one they offered me so far), diving can be tiring, yet I'm a chunky 50-year old out-of-shape white collar worker. How do I do it when some of the youngsters skip dives to take breaks? Nap! Even if it's just sitting somewhere with your eyes closed 10 or 15 minutes.
4.) Get some swimmer's ear prevention drops, and use them every few dives. Don't wait till you need them, or they will burn miserably. Bring enough to share.
5.) Never mind photo-editing; bring an iPad, smart phone, laptop or similar to back photos up to each evening in case your camera floods during the trip. And yes, a glance at your photos may alert you the exposure control knob got accidentally turned and your latest photos were too dark, etc...
6.) After your dive, everyone will leave their gear at their station, disconnect their 1st stage to ready for a tank refill, and go get a snack or ready for the upcoming meal. Once the dive deck is clear, and you've had your snack or meal, go to the dive deck and test your nitrox mix while the deck is almost empty, and log your % (they'll likely have a clipboard for this). Saves waiting.
So, rest yourself often, protect your ears (e.g.: if you like Sudafed 24-hour to aid equalizing/Flonase/etc..., bring it!), back up your photos and don't clog the john.
