If you're prone to motion sickness and are unsure how you will react on the ship- start taking Bonine (one a day) about 2 or 3 days before the cruise and continue all the way through the cruise and up to a couple days after you're back on land.
Seabands work for many too- they helped my DH enormously.

(They sell them on board in the gift shop if you forget to bring them with you)
Bonine worked wonderfully for me as I am very sensitive to motion. (my biggest probalem was ataully AFTER the cruise back in WDW!! I still felt the movement of the ship for days afterward)