Install the skin on a solid surface and away from a dusty environment, as well as a bright light condition to check for bubbles. Make sure you apply a lot of solution so you can slide the skin to the position you want it to. If you have the palm rest skin than I would advise you to be as CAREFUL as possible because if it gets into the speaker grills, keyboard, and ESPECIALLY the trackpad, your not gonna be happy with the results. Also, if you have a trackpad protector skin you should NOT install it, through two personal experiences I had the solution pass through the edges of the trackpad and it caused a loose clicking sound, which I exchanged both and will never do it again. In addition, always have a towel near by to wipe the edges and leftover solution right away so it doesn't get into the system.
You made Apple cover the cost of 2 laptops because you screwed up while applying a skin?? Pathetic...no wonder return programs are so strict/non-existant...