I always had trouble applying Kapton tape to the print bed, specially when using full width tape, now I think I have the technique down pat and thought to share it.

You need a large (at least twice and a half times the size of your print bed), clean and flat surface to work on, put down the print bed on one side, get the Kapton, a squeegee (or plastic card) and a bottle of window cleaner.
Spray the window cleaner on the table next to the print bed... hang on, there's method to this madness...
Unroll the Kapton tape, a little longer than the print bed, spray the sticky side with the window cleaner, then lay it down sticky side up over the wet table and cut it, the surface tension will keep it flat and the liquid on the sticky side will keep static electricity from sucking up dust particles in the air.
Now spray the print bed with the window cleaner, a sloppy job is a good job, then flip over the Kapton over the print bed, slide it around until if fits right and get the squeegee, squirt some cleaner on top to help the squeegee slide, and starting from the center squeeze from the center out, don't go back and forth, one stroke at a time always outwards and next to your previous stroke.

The edges may not want to stick because the Kapton sucks up liquid from the edge of the print bed under the film, so cut the excess Kapton, soak up the liquid with a paper towel and wait until the rest dries out, then you can squeeze down the edges down.

Done properly it takes only a few minutes and it leaves no bubbles or dirt under the Kapton

Hope that helps!