I am assuming that you will be booking thru the RCCL website.
I have booked tours on two different ways; one waiting to get onto the ship (and waiting on line and being disappointed when the tour is sold out)and two booking on-line.
We have found that booking on-line is extremely convenient. I first have the t.a. print out all the excursions offered for that cruise. My husband and I then go over the hard copy and then make our decision. After that, we go on-line to the RCCL website and pick the shore excurions. It does take awhile before the RCCL excursions are available on-line, but be patient as you can sometimes choose the most convenient time if the tours have a couple of different times when they start the tours. Also, you pay for the excursions on-line as well with a credit card. Once you have paid, you will get confirmations on all the tours and when you get to your stateroom your tickets will be waiting for you!
Hope this answers your question.
Big Red Boat
Carnival Valour 2004
Carnival Jubilee 2005
RCCL Empress of the Seas 2006
RCCL Brillance of the Seas 2007
RCCL Grandeur of the Seas 2007
RCCL Jewel of the Seas 2008
RCCL Explorer of the Seas 2008
RCCL Explorer of the Seas 2009
RCCL Grandeur of the Seas 2009