What's the best, easiest way to paint paneling?

https://www.youtube.com/watch?v=5FJ1jmKzqt4

Clean, prime, paint. Have also seen people glue rope from Top to bottom to cover the lines in the paneling to disguise it then paint.

We have a log cabin and too much wood is dark and dreary.

We are quite pleased the previous homeowner placed paneling in two bedrooms and painted it a light color. I would suggest not to hesitare to paint paneling for a room brightening update.Prime and paints. We left the grooves in place, some prefer to spackle them level.

Scrub the paneling with a good cleaner/degreaser. Fill all nail holes with wood filler. If the paneling has deep or rough grooves then caulk them. One coat of primer and then two-ish coats of paint. I would NOT skip the primer for a two in one for old wood paneling. It would look best sprayed, but if you don't have access to a sprayer you can roll with a very smooth nap roller.

Prime first, then paint. We did this in the upstairs of our present home in a very light beige, in fact, we couldn't afford to dry wall three bedrooms, so this worked for us. Ours was not dark, but medium tan and very good paneling.

We never filled our paneling with anything and it looks great.

Clean it, rough up the surface a bit with sandpaper, then use a good quality primer/paint in the color of your choice.