I've tinted about 5 cars now. Did my truck 3 times after tint started fading. Precut does take alot of the time out of it. Here's some pointers:
1. DO NOT use Windex or any amonia-based cleaner. Ammonia will loosen the glue. In fact that's what I use to strip the windows when I redo the tint.
2. Like Vic said, make sure you clean the window good before you lay the film on it. Any little spec of dirt or dust will cause a small bubble and be stuck there for as long as you have your tint.
3. Have plenty of solution (soapy water). Spray plenty on the glass and on both sides of the film. It makes it alot more manageable and acts like a lubricant when you're working with it.
4. Don't squeegee the film until you are absolutely sure you have it where you want it.
Here's something I do on my truck, but you don't have to if you don't feel like it:
Take the weather strip off of the bottom of the window and squeagee the tint a little lower. Not sure if you're precut stuff will be long enough, but that's what I do with the rolls I use.
Like I said, they're already cut, so that saves you a good deal of swear words. Good luck!
Just remembered a few other things. If you can, get a hairdryer after your done and run it across your windows. For some reason it seems to help it stick better. Also, I believe some of the pros use heat guns, so a blow dryer is the closest thing that most of us have lying around the house. When you are done try not to roll down your windows for at least a day.
"Any man who says he is an American, but something else also, isn't an American at all. We have room for but one flag, the American flag... We have room for but one language here, and that is the English language... and we have room for but one sole loyalty and that is a loyalty to the American people." - Teddy Roosevelt