You should book a "room only" reservation as soon as you know when you'll be traveling, so that you are sure you have a room at the time you want to travel. Disney allows resort bookings up to 550 days in advance. Just contact a travel agent or call the Disney Reservations Center at (407) W-DISNEY (934-7639) and make a "room only" reservation.
If you belong to the Auto Club, you might as well see if you can get the AAA discount on your "room only" reservation now, in case nothing better comes along.
"Room only" reservations can usually be changed later to reflect any discount codes or Annual Passholder discounts, if they become available. However, only a certain number of discounted rooms are released for each code or discount. If those are all taken when you call, you will not be able to switch to the discounted rate, even though you already have a reservation.
If a discounted package is released later and you are interested in changing from "room only" to a package, you may have to book the package and then cancel the "room only" reservation.
Don't book a full-price package now if you are planning to look for "room only" discounts later. All packages have restrictive rules about cancellations and changes. Also, some of the package elements (especially airfare and insurance) are usually nonrefundable.