Are you trying to install them dry? Get a spray bottle and fill it with water, then add 1-2 drops of dish soap. Shake up the bottle before using it, and spray the fender really well before laying down the stripe, the water/soap mix will give you more time to move the decal around before it adheres to the fender. As far as a guide, just make sure they look straight up and down the fender. You can use the horizontal line of the fender and the angled line of the fender flare as reference points. You'll want to put a long piece of tape at the bottom or top part of the decal to keep it in place as you press the the stripe down with a decal squeegee or credit card. You should have enough time to work the decal to get all the air bubbles out, this will take some patience to get right, don't overwork the stripe too much. You can always go back and pop some of the smaller bubbles with a razor blade. I started with the bottom section of the decal and worked my way up. The top part was pretty easy to do once you have the bottom on and lined up, you'll just need to fold/cut the access of the decal into the hood area. Make sure to take off your antenna and mount on the passenger side before installing the decal on that side. I always like to let the decal fully dry for 30 mins before removing the top paper, wet the top paper before trying to remove it. If you pull the top paper at an angle flat across the decal it won't pull the decal up. Check out Omelet's build for pics, he always does a good job showing How-To's.
05 Jeep Grand Cherokee: ORT 4X4; Khaki #55
Too many mod's to list...