I wouldn't use spit. It contains bacteria that can cause the decal to deteriorate over time.
Apply a gloss coat. Let dry for 24 hours.
Apply the decals. Let dry for 24 hours.
Apply a gloss coat. Let dry for 24 hours.
Weather.
Apply flat coat.
I like to use MicroSet and MicroSol and I add a bit of Elmer's glue to my decaling water.