You won't even be able to book those flights for a couple of weeks at the earliest, since the legacy carriers (American, Delta, United, USAir, etc.) don't open for reservations until 330 days out. That means to book a round trip with a return on Jan. 5, you'll have to wait until about Feb. 9. Other airlines, like Southwest, don't open their schedules up until later (usually about six months out, but sometimes later).
Once you can start checking fares for your dates, I generally just go to one of the big sites like Expedia or Travelocity to get a sense of times, connections and fares. That way you have at least a general sense of what your options will be so that you can evaluate prices going forward. Unless you have to fly on a specific flight on a specific day or have reason to believe that all flights will be sold out right away, however, you shouldn't book now.
After that, you can check back on Expedia or Travelocity to keep tabs on how rates are moving. You also can sign up to get fare sale announcements from the airlines that can get you from Austin to Orlando. Most of them allow you to register for those updates on their Web sites. That way you'll know if any deals are out and can see what "good" rates might look like. There probably won't be any sales for your time period until later in the year, however, and given that you're leaving in the middle of the holiday period there might not be much in the way of sale fares regardless.
Southwest does fly out of Austin and maybe other discounters do too. As a result, I would try to wait until their fares come out (maybe April/May/June, but not for certain) before booking anything. With Southwest, you also can install their DING service to get special fares delivered directly to your computer.
Good luck!
