This might help when using Model Master tape:
Usage/Tips:
1) Watch out! Low adhesion can cause applied paint to seep under edges. To prevent this from ruining your paint jobs:
a) Spray paint from an angle where mist does not gather at edge where tape meets surface.
b) On a two-tone paint job, paint the first color, let dry thoroughly. Mask, then shoot the same color lightly to seal any points at which seepage would occur. Let dry. Now spray the second color. - Viola!
The above comes from Testors Modeler's Technical Guide.
Jesse