After applying Blue Batmobile's vinyl this weekend, I've gotten pretty handy with applying stickers.
Put some dish soap and water in a spray bottle.
Do one letter at a time.
I used a hair drier to warm up the plastic and the vinyl a bit. It's easier to place when flexible.
Spray some soap water over the letter you're about to do, peel off that letter and insert it in the recessed area. Because of the soap water, you can slide it around and place it perfectly without the adhesive sticking.
Once you get it right where you want it, you can press the water out. I used the corner of a credit card and a finger.
If it doesnt fit perfectly, you can warm it up with the hair drier and stretch it into place nicely.