A couple of important tips to keep in mind:
1. You can get one FASTPASS per park ticket. You will need to "scan" each park pass in order to acquire a FASTPASS.
2. One cannot acquire another FASTPASS until the current one you have is in effect. For example, if your FASTPASS says to return between 1:00 PM and 1:20 PM you cannot get another FASTPASS (even for another attraction) until 1:00 PM. A time stamp is printed on the bottom of your pass and indicates when you may get another FASTPASS Many guests think that they can simply run from one FASTPASS attraction to another and accumulate passes.
3. Remember to always look at the "Stand By Time" and the "FASTPASS Time." Many guests will simply get a FASTPASS and not look to see how long the actual line is. I have on many occassions, jumped on a favorite attractions when the line is short and then obtained a FASTPASS for later in the day when I get off.