Paint walls from the top down. If you are using a roller, start by making a large "V" or "W" (3'x3'). Then fill in between the gaps, blending into your initial stokes. Always work from the unpainted into the painted area.
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.