If they're vinyl stickers as most seem to be first step is mark the area on the frame where the decal will go, you can use pieces of masking tape to mark where the top and bottom should be. Then wipe the frame with a weak soap/water solution to clean it, then immediately before applying the decal wet the frame (not the decal) well with the same solution...get it good and wet, this will allow you to move the decals around a bit till they're perfectly aligned. Peel the backing off the sticky side of the decal and apply. When they're where you want them use a soft cloth to squeegee any water from underneath. If your decals have vinyl on the top wait for an hour or two before carefully peeling it off, start at a corner and gently work it off making sure that the decal doesn't lift off the frame and voila, you're done. You should then wait at least a week before clearcoating to make sure any remaining water trapped under the decal has dried completely.