If you're a first time cruiser or it's been a while since you've done it, you may not know some of the neat little tricks regarding booking a cruise. There's a bunch of great forums at cruisecritic.com which can give you tons of tips, but if you don't have time to read it right now I'll give you the highlights Cruise Forums Royal Caribbean .
First, book early. If you don't live right next to the port you'll want to book early so you can secure a good price on your airfare. The other advantage is that you get a better pick of cabins. Where you want the cabin location depends on your personality, but in general you'll want something in the middle (bow to stern and top to bottom) if you don't want to feel much movement. You likely won't feel much anyway, but if you're concerned about it go midship. Also, with Royal Caribbean, even if you've already booked, you can still get a refund on the price if the cost of your room category drops in price, as long as you haven't made your final payment yet. So if you book a balcony cabin a year early and pay $1200 per person, and three months later the price has dropped to $1000 per person, you get a $200 per person drop in final price. You can choose have that $400 savings applied as on board credit for your trip, or they can take it off the balance of the final amount due. Take note, the cruise line won't automatically drop the price, you have to notice this and call them. It pays to keep checking on the prices even after you've booked.
If you book through a travel agent you can't call the cruise line about your reservation to make any changes (including price drops). All those requests must come through the travel agent. This is OK if you have a good relationship, otherwise it can be a real pain.
The travel agent cannot cheapen the cost of the cruise and charge you less than if you booked direct. However, they can and often do offer you other benefits such as on board credits, free gratuities already paid, or discount excursions. One tip I've learned from the forums is that you can book direct with the cruiseline initially and then when you're ready to make final payment transfer the reservation to a travel agent who is willing to give you discounts. The agent still gets their commissions and you get the power of requesting your own price drops up to the transfer, plus the benefits of the extra credits from the agent. It's a win-win situation.