either the windex spray will work, the dish soap and water, or you can buy a commercial gel to apply the decals, tho the gel is spendy. we use the gel if its a big decal or stripe thats picey. (kind of like the old firebird hood decal. i like to use a 3m rubber squeegee to float the liquid out once in place. start from the center and squeegee out. if you get a tiny air bubble and cant squeegee it out, use a stick pin to pop the bubble and squeegee flat. here are the squeegees. any body shop supply can get them, only a couple dollars. and they wont tear the decal!!