From the Microscale Decal website FAQ section:
Basic Instructions for the Application of Microscale Waterslide Decals
1. The object to be decaled must have a clean and relatively smooth glossy surface.
2. Cut out the Decal lettering and dip in clean water (preferably Distilled water) anywhere from 10 to 20 seconds. Note: Some lettering might take a longer soaking time than other sheets. Set the Decal on a damp paper towel for a short period of time or until the Decal slides freely on the backing paper.
3. Place Decal where desired on object. It might be of help if a layer of Micro-Set is brushed on the object first and then place the Decal. This process will allow the Decal to avoid the Silvering effect that can happen with just the water. Work as fast as you can in placing the lettering as the Micro-Set starts the wrinkling of the Decal and setting it to the object.
4. Blot gently around the edges of the Decal with a paper towel or tissue to remove excess water and allow to dry completely. Add more Micro-Set as necessary over the top of the Decal very carefully. This process will make the Decal lettering a part of the model.
5. When placing a Decal on slightly irregular surfaces, use Micro-Sol. This is the stronger of the two products and aids in soften the Decal to fill the contour, rivets and crevices on the object. The setting solution also improves adhesion by eliminating the tiny bubbles that can be trapped under the Decal film.
6. When the Decals are completely dry, it is necessary to wash off the Decal glue and water spots from the object with a damp paper towel or you may brush the water on and then dab it dry. Do not wipe the Decal lettering. Drying time may vary, but allow several hours or overnight to before proceeding.
7. It is recommended that a clear protective coating be applied to the entire surface of the object. The over spraying of the Decals will protect them from handling and seal the painted surface.
Matt