start reading the forums and you will get a world of information.
if you list a few specific questions you have, then people will answer them for you.
First things I would recommend starting with is which itinerary you are interested in (which will also set the number of days for your cruise), when you want to go and which ship do you want to be on if there are multiple choices?
Next would be researching and selecting your cabin(s).
Finally, you can start to look at dining, spa, excursions, kids clubs, etc.
Just my opinion. Good luck.