Congtrats on your first cruise. I would read all the info you can, you can check out the First Time cruisers here at Cruisemates to get all the tips you will need.
As for shore excursions, go to the Royal Caribbwean web-site and look through them all and get a feel for what you want to do, many to choose from. If there is anything that you truly want to do, I'd suggest to pre-book it before you go. You can do that usually by 60 days before your cruise.
Also, remember that while on the ship, you will be using your sign/sail card for all your purchases, no cash is involved. They will charge your credit card at the end of the cruise for all the purchases you had. Keep an eye on those, they add up rather quickly.