My birthday is this summer I want to go on my very first cruise, what is good?

I like the tropics.
When should I book?

I have been on about 20 cruises with four different cruise lines and here's what I suggest.

The cruise line that has the best on-board activities and does cruises all over the Caribbean where you want to go is Royal Caribbean. That cruise line has a variety of cruise itineraries from several ports in Florida and Puerto Rico. You can get a balcony cabin (which is a real plus) for somewhere in the neighborhood of $1,000 or less on several cruises from these ports. Other cabins are as low as about $600 per person. The earlier you book the better and also look for the special deals. You have your option of the Eastern, Western, or Southern Caribbean itineraries. Take a look at this web link:

http://www.royalcaribbean.com/findacruis...

The prices shown are per person based on double occupancy (that means two people must go). That price includes your cabin, all meals and entertainment on ship, free use of all of the facilities on ship except the spa (you can use the gym free but have to pay if you want massages and things like that). There will be some additional charges such as the $10. per person gratuity fee per person per day ($70 each for the week), and if you buy soft drinks or alcoholic beverages you must pay for them. Then you pay for any photos, souvenirs, and any tours you decide to take from the ship (you do not have to do any of these and you can get on and off the ship in ports all you want without doing a tour.

So, I recommend that you book one of the Royal Caribbean cruises; I have been on most of the ships shown on the web link I gave you and you will have great fun.

The right cruise really depends on what you like. You can get tropics in either the Caribbean or the west coast of Mexico, which one is better depends on what's convenient to where you live.

To over-simplify, if you want nightlife and a social atmosphere, go with Carnival. RCI and Princess are also good, lower-priced options.

This guide to choosing a cruise, based on what matters most to you (type of service, activities, etc.), might help you:
http://www.cruisesavvy.com/savvyguide/ch...

In terms of when to book, if you want to go this summer, and you want to be sure you get a good ship and cabin, I'd book ASAP. This article explains about the pros and cons of early vs. late booking:
http://www.cruisesavvy.com/savvyguide/bu...

Happy upcoming birthday!

What cruise you take depends on what you like to do and just how old you are. There are party boats like Carnival, family boats like Big Red Disney Ship, and other companies are for older clientel. There are cruises for many different groups like Christian cruises, Gay cruises, etc.
The best way to do a cruise is not by the internet, but by going to a travel agent who specializes in cruises. I know, I tried to do it on the internet and just wasn't sure. The agent got better prices and the right "style" of cruise for us. (older and quieter).
Booking early is the best....often times cheaper and the best cabins.