Limited time so a fast post.
Start in the corners, do all four first.
Then each consecutive staple is used to divide the long straight segments approximately in half centering the slack and adding a hair of "stretch".
As you keep stapling in the center of each open segment, you will eventually end up with evenly spaced staples all the way around and no folds or concentrated areas of excess material.
It's a bit of an art, may take a bit of trial and error to find the right amount of stretch for the material you're using, but be persistent and by the time you do all four grills you'll be an expert.
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