Being your first cruise, you won't know for sure what you consider a "good" cabin until after you have tried it. Oceanviews are fine, but in all honesty, most of your time will be spent somewhere besides the cabin. You are in there to sleep and change clothes. So I would not get too fussy over the cabin. Oceanviews are fairly consistent.
My suggestion is to have your travel agent (or Carnival Cruise Specialist if you are using them) book a Oceanview "Gaurantee" (sometimes called a "to be assigned" cabin). Tell them you want a minimum category that will give you an unobstructed oceanview cabin. That way you get a good cabin and have the chance of getting an upgrade to a better cabin. Maybe even a balcony room if they quickly fill the ship.
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise
NCL Dream October 2006, RCCL Mariner OTS June 2007, Celebrity Silhouette 2013