If your extension cord gets tangled up, don't pull on the ends. Instead, gently loosen all the tighter snarls in the middle until them become larger loops that can easily be untangled. A way to avoid tangles is to use a retractable cord reel. It will let you reel out only the amount of cord you need, then quickly reel it back when you're done.
As a final check when taping drywall joints, use a side light to check for smoothness. The light can be a halogen worklight, a troublelight, a lamp without a shade, even a larger flashlight. Hold the light close to the wall next to the joints in several places to reveal high and low spots, or bumps and depressions, that otherwise would be easily missed.