How to paint cabinets

Clean them thoroughly with TSP. Then rinse.

Then wipe them with white rubbing alcohol.

Then sand them with an electric sander; stay in the direction of the grain. Wipe down.

Wipe down with rubbing alcohol again.

Buy a top-of-the-line paint that is recommended for strength. I recommend PPG Porter Paint's Advantage 900 in semi-gloss. Buy a high quality paint brush(es).

Paint in direction of grain. Let each coat dry overnight.

Very, very, lightly sand in between coats; close your eyes and feel with your hands. (If you feel a "tooth" then it needs to be lightly sanded with a FINE grade sanding sponge.)

Changing from dark to light, you can expect 3 - 5 coats.

No top coat needed if you use Advantage 900.

I would give them a good cleaning, with TSP (at the hardware store) to get any grease/oil stains out, then lightly sand them and refinish them the way you want.

It's easier to paint doors and drawer fronts if you take them out and lay them flat, then you can paint the cabinet bases and re install the doors without painting around them.

Be sure to thoroughly clean your cabinets first. Sand with a fine grit sandpaper and wipe clean. You can then varathane with at least two coats.

If you want to paint over them you should use ESP Primer, then undercoat and then Top coat...

They certainly have to be cleaned first then lightly sanded and cleaned again. Then a good primer used and you can paint away. Be sure the paint and primer can be used together.