Precut is easy. Just make sure you center them properly and make sure the edges are firmly pressed into the clear parts so no paint gets underneath.
If using non-precut, I'll cover the glazed area with Tamiya tape cut larger than the panel to be masked. I try to get at least one edge to line up with the panel edge to minimize cuts, preferably two. Press the tape down firmly so that the raised frame shows up and then very carefully cut with a brand new Xacto blade lightly along the remaining edges. I usually try to make the first cut along the center of the frame and remove the excess tape so the frame edge is easier to see. Then I'll go back and trim along the edge of the frame. The trickiest part is to not cut too deep. You want to avoid scratching the glazed panel and slips are definitely not in the plan. Work slowly and carefully. For something with lots of frames like the Condor, you may want to do a little at a time and take breaks because it is very teadious work in my opinion.