Dwayne gave you the ultimate in drink price prep guide. So I won't go into those details, but here are a couple of tips on drinking-
If you are a beer drinker, go for the Lidp deck and get the bucket. Worst case you don't drink them all and you take the unopended bottles back to the cabin and ask the steward to clear a space in your mini fridge for them (be sure to do that or they will charge you for drinks from the mini fridge even if you didn't take them. In fact you can ASK the steward to clear it out at the beginning of the cruise and then you can use it as needed. Not all stewards will do this, but you can ask (and a little extra tipping helps here too)
The other tip is DON'T get the drinks in the souvenir "glass". Its really a plastic cup (they used to be nice glasses, but I haven't seen those in years.). You spend an extra $2 per drink and have all these plastic glasses that you wind up throwing out because you can't pack them or end up using cabinet space back home. Any drink that they have in a souvenir glass they can make in a standard glass and it will be less expensive. If you are not sure, ask the waiter about the prices.
And third and last tip- 15% gratuity is added onto each drink order. It will be on your receipt. The receipt will have a line on it for "tip" like a charge card restaurant receipt.
Unless you intend on giving an EXTRA tip, don't put anything on that line (or 0 it out) as that 15% is already in the price. That goes for all the places you order drinks from on the ship.
You will have a bar waiter assigned to your dinning room table. Sometimes these guys are really good and I will give them an extra tip because they go out of there way for us -knowing that I always want a particular drink for dinner and having it waiting or making special drinks that are not on the menu (the wife likes a drink called "Kiss on the Lips" that was a CCL drink special once and they don't always have it.) Or they will just provide extra good service... Then I give them a little extra tip, but most of the time the drink waiters are are just getting a drink for you...
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise
NCL Dream October 2006, RCCL Mariner OTS June 2007