If you pay in advance those looking after will know, you may in this type of situation give a bit more if the service you have received was above what you expected from your waiter or stateroom attendant etc. otherwise at the end of the cruise you will receive envelopes and advise on the going rate for those you are expected to tip and you do this on usually the last night. You might agree onboard to prepay your tips and in this case the cost is added to your stateroom account you settle before you leave the ship. Finally yes you can give a daily tip and there are possibly only a few of those say if you can have your breakfast delivered to your stateroom and it is good order and comes on time then this might be an option. As far as drinks are concerned there is 15% added every time you place an order, but keep all the receipts in case you have a query on your account when ever this is supplied, normally the night before you leave the ship.