Cover the top of the sticker with masking tape, overlaping the edges of the sticker
Pull the back off the sticker
Spray the adhesive surface and the area you're applying the sticker to with slighly soapy water
Apply the sticker, sliding it around until it is exactly where you want it
When you have it in position, use something with a firm straight edge (ruler, credit card, etc) to squeeze the water out from under the sticker
Carefully peel back the masking tape, and you're done!
From: http://www.tradetricks.org/archives/2005_05.html