The common practice is to place you tips in the envelopes that wll be provided in your stateroom and give them to the individuals on the last night of the cruise. You will get the envelopes a day ahead. IF you choose to charge your tips, you fill in the charge form and take it to guest services. They then give you receipts which are in 2 parts--one part you keep, the other you place in the envelope for the server.
We have checked with the servers in the past, and they do receive 100% of what you charge (
DCL does not deduct a handling fee or anything.) It is easier for them to receive tips this way, as they get a check every 2 weeks rather than keeping track of cash.
You also tip room service when they come to the room (a couple dollars, depending on size of order).
I'm not sure what you mean by "pre-pay your tips", but what I've described is the norm.
I use the tipping guidelines as a starting point. Since we are used to getting service well beyond the norm, I usually tip more than this. I guess if the service was crummy, I might be tempted to tip less, but this has never happened on DCL. I try to keep in mind that many of the servers are supporting families "back home" and remember how very blessed I am to live where I do and take a cruise--they count on tip income .... It is fine to do a small gift in addition to $ for the people who normally receive tips, but a gift should not be done instead of $.
For people who are not normally tipped (like kid counsellors), you might want to consider a small gift (like a phone card.) These people are not allowed to accept cash. There are about 12 counsellors in each the club and lab, so you might want to ask your children who was really special to them, and do a small gift for that person. Obviously, this is not required, but is a nice touch. My DD usually identifies one or 2 counsellors that she felt were "the best" and we enclose a short note from her.
You'll have a great time.....