spring plug first and last
The easiest way I know of to avoid carelessly scratching your pistol is to remove tension from the slide by removing the spring plug first then remove the slide stop lever. My Mi-Spec Loaded was the test dummy for this learned lesson.
When assembling your pistol, put your slide on with barrel, spring and spring guide installed; push it back on the frame until you see the barrel link lined up with the hole; partially insert the slide stop so that it engages the barrel link; push slide back on frame until the slide stop groove and hole are lined up; then carefully position slide stop against plunger and firmly press slide stop where it belongs.
Now it is time to push the spring plug in place and rotate your bushing counter clockwise to the proper position.
It was a lesson learned for me although I admit to not being an idiot, just over-zealous and impatient.
My Mil-Spec Loaded is full of handling marks and those caused by carelessness. My Mil-Spec 38 super, Mil-Spec .45, and DW pointman 7 show signs of handling, and shooting but not carelessness.
Good Luck.