Download/install Ding!, but understand that you have to check it regularly during the day for it to help.
Watch your flights everyday, and at different times of the day. Prices go up and down constantly, so be prepared to grab them if you see a flight at a price you like.
After you've reserved & paid for your flights, it's always worth watching Ding and the website to see if the price has gone down, because you can easily change the flight for no fee. Just cancel the old flight, which puts your money into a credit with a code number; then reserve the new flight (or same flight with new price) with that code number. The balance of your money will sit in that reserve account with that same code number until you use it on another flight.
Get on the website exactly 24 hours before the flight is scheduled to depart, and check-in. This will assign you an earlier place in line to board the plane and choose your seat(s). A tickets go first, then the B's, then the C's. At the gate, they ask the A's to line up in numerical order according to the posts on the floor. After the A's are on, they have the B's line up in numerical order. Of course, if you've got a wheel-chair or small children, you can board before the A's.
Southwest is my FAVORITE way to fly!!! Enjoy your trip!