Some say soapy water is the best, but detergent solutions really seem to work just as well. I use Windex just because there’s a bottle right there on my bench. This works great with pressure-sensitive decals too.

Spray the surface with the solution, lay the decal (or trim strip) in place, and slide it around until you’re happy with the location. You can lift and re-position as much as you need. Once you’re sure it’s right, go back over the surface with a paper towel, blotting away as much moisture as you can. Then let it dry.

No bubbles, no stress, and they’ll stick forever.