I have roughly 20 dives off of charter boats so not a veteran by any means. That said I have done wreck dives in SC, MX and a few other places. Here is what i have learned/observed .. Much of this was hit on already but starting from the beginning when you get to the site.. Also taking your question as an overall one - not just air consumption as in my opinion all the below affects buddies on the dive.
**if, like me, you suffer from sea sickness get the meds, bracelets,,whatever well in advance (day before) and do your best not to become a liability to your self and others on the boat - sometimes this does not work for me but make a concerted effort to take care of it to the extent you can** So far I only fed the fish once ..it's not pleasant for others while they chow down a sandwich on the SI. **
1. Get there early - do not be that guy that arrives late / last minute and the boat has to wait while you run across the parking lot - seen someone have to do it and let's just say they did not make friends that day. Most boat captains will leave anyway but again if you are last minute but not late they will wait, but it's just a rush that is not necessary. Kinda like that guy/gal running through Ohare airport to get to the gate. If you can avoid this ..do so .. your dive will end up being more relaxed and enjoyable.
2. Ask the captain for permission to bring your equipment on board. My first charter I did not do so and was reminded it was proper etiquette. have not forgotten since.
3. Have your equipment well thought out the night / day before. Boat charter is not the place to make drastic changes to equipment to the extent that they have a serious impact on buoyancy. Example I dive HP100's and and hp133 for deep quarry dives in 100+water. I know my weight based on my BP/W and current setup with a 7mm suit. If I go on a boat dive and decide to dive AL80's with a shorty then I need to know what the weight swing is and plan accordingly. You do not want to backroll and find out you can't get under. Reason I bring it up is folks are suggesting (and I agree 100%) to perhaps switch to an HP100. Bottom line have your rig set, dialed in, know your
4. If you don't do #3 above and come prepared you may have the boat captain do it for you. On my 2nd boat dive (by then I had already 30+quarry dives on HP100's) I decided to go with an AL80. I had not done step 3 above on the tank swap yet I know the weight swing was somewhere in the 6-8 lb range. Because I did not come across as "prepared" the captain proceeded to tell me i need to dive with 20 lbs of weight. now I weighed 220 at the time but I have been lifting for years and at the time( sadly no longer) was way more muscle than fat). I could have used 15 lbs and done great as I was overweighted with 20. On the 2nd dive there was an instructor whom I had voiced my concern to and she went to the captain and vouched that she had seen me overweighted. I dove with 16 lbs on the 2nd tank dive and was perfect. Being prepared will make the crew and divemaster see that you have done your home work. If they think you are a risk they will make decisions for you. you may or may not agree/like them.
5. Pick a spot for your stuff and keep it organized. If you have to rent stuff do so but I suggest always brining your own, Primary reg and 2nd, fins, etc etc..and in my case a 19 inch or 30 in ch pony depending on the dive. The more stuff is yours the more you will be familiar with it. As a side note I always dive a pony bottle and will never dive without one. I suggest you invest in one. Being left alone on the anchor line is not cool. Nor is ascending or diving by yourself in general. Had many an insta buddy disappear on me with little to no regard for where I was. Guess what I had a pony with me with enough air to make a safe ascent and safety stop so bye bye buddy. That is also why I am enrolled in a solo class and I encourage you to do the same as you expressed interest in it. On all if not most of my boat dives I realized i was in essence diving alone. Whether they pair you with the guy show is spearing fish and totally forgets you are there, the newer diver who would not be able to help you anyway probably, or the more experienced diver. Others will disagree but I think its on you to be able to get your self topside safely in the event of an accident/malfunction. It's your life at stake do you want to trust a stranger with it?
6. Just be friendly as most divers are. I usually bring extra fresh cold fruit in a cooler and share in between dives. Made many dive buddies at boat dives just by saying hi, sharing dive experiences and getting to know people. Not saying you need to feed the charter just saying a friendly handshake goes a long way. As you talk the people and introduce yourself they will do the same and you will quickly see whom you have chemistry with. On almost all my boat dives I had found an insta buddy before the captain asked who was diving with whom. Although an insta buddy by the time I got in the water i already had discussed specifics of the dive. who would lead, follow, OOA sharing options, etc.. This will make you feel more comfortable when you start your first dive.
The rest has all been said...