How to solder wires to a hobby motor
It's probably better not to tin the lug before you solder to it, instead just brighten it up by scraping it with a razor blade or using some fine sandpaper.

The hemostat will act like a heat sink and suck up the heat that would normally melt the plastic, but only for a little while, so the main thing to remember is to get the soldering at the lug done quickly and use flux cored tin/lead eutectic (Sn63/Pb37) solder if you've got it. If you don't, soldier on with what you've got...