I had a Jeep Wagoneer with nice flat window panes everywhere and it was cake. With the defroster back window I just used a lot more water than I thought necessary and went with the squeegee. The trick is to go with the lines from left to right, not up and down. IF you have a heat gun you can make it adhere a little better.
On my 5'er, I was going to tackle it myself, but I looked, and looked and looked... and figured... well.. its curved 3 ways, and its not exactly "square" in shape AND I have defroster lines and antenna lines to mess with... lets leave it to the pro's (especially since they have sheets wider than the stuff you can buy in boxes at the parts houses so they can do it with 1 sheet rather than using two and trying to line them up together).
Had my whole car done for 120 bucks with warranty. The hardest one, back window came out the best, and I had to have 1 door redone due to peeling a month after install. The back window had these watery pockets in between the defroster lines for about 3 days, but I was told to just leave it alone for about a week and not roll down the windows. I let the car sit outside in the 100+ degree sun for 5 days, and wouldn't ya know it.. the water was gone, the tint was tight, and I have no bubbles anywhere. Shop around and leave it to someone else that'll warranty the work if you can shell out a few extra bucks.