This is going to be as much as a step by step of my way of doing things. It may be right, may be wrong. I'm self taught so don't take anything you see me do as "gospel".
The first thing I did was mount and trim the body to what I considered perfection. I got some help from Jeff (GoMachV) regarding the easy way to cut for the front body mount post. You can find that thread in this section of the forum. All the edges of the body are sanded/near polished. Most tears in lexan start from a rough edge so I make sure that my edges are perfect before even thinking about painting.
These are my basic tools for masking...
Metric steel rulers
Tamiya scissors (very sharp and precise)
Red Sharpie pen (you might like a different color)
Cut down x-acto knife with #11 blade (cutting the handle down makes it easy to get around inside the body)
Tape- I'm using some wide, Tamiya like tape that I bought years ago. It's branded as KAMOI TAPE.

I use the Sharpie pen to outline (on the outside of the body) the area I want to mask for no paint. I burnish (rub down) the tape well, then follow the Sharpie outline on the inside the best I can with the knife. I don't use a lot of pressure and try not to depend on the tip of the blade to make the cut. Cutting mostly with the tip can cause a ragged edge. I use a new blade for each window, that's just my preference.


Once all my masks are cut out I'll use some denatured alcohol to remove all the Sharpie pen outlines.
This thread will continue as I move on to the next step, masking for graphics.