With all of those doors, I have developed a technique that works for me. Some people like to remove the doors from the hinges, drive nails into the tops and bottoms, and use saw horses in the garage to paint them. I don't have that kind of time, patience, or space, so I leave the doors hanging right where they are. I usually end up painting 2 doors at a time. I paint the first coat on one door and then, while it's drying, I paint the first coat on the second door. Then, while that's drying, I put a second coat on the first door. You get the idea.
First, gather your supplies: you'll need a good brush (I can't stress the importance of a good-quality brush)! You'll also need tape, a smooth-surface roller, a paint tray, painter's plastic (to protect the floor) and of course, paint! I used semi-gloss.
My husband had already painted the trim, so then it was my turn to tackle the doors. Tape off the hinges and knobs.
Then I cover the horizontal parts.
Next, I move on to the middle of the door.
Take your brush and get into the grooves! I've found that if you really load it up with paint (not quite dripping -- but almost) you can get a really smooth look. Pull the brush straight down in one long stroke. If you run out of paint before you run out of door, reload and start about an inch above where you ran out. When I do it this way, I avoid brush/bristle marks in the paint.
Don't forget the sides! Keep a damp cloth handy to wipe off the hardware if you get paint on it -- and I always do! Once the first coat dries, go back and add a second coat.
I learned a neat little trick from the guys at the paint store. If you're done painting for the time being, simply wrap your roller and paint brush in plastic wrap. This is a great little time saver! It always takes me a good 10 minutes to wash everything out, so by doing this, I'm saving time and paint. When I unwrap them, they're good to go again. I've left them like this for as long as 24 hours and didn't have a problem.
Once you're all done, stand back and admire your handiwork!
The first door I did took me a few hours -- I'm a bit of perfectionist when it comes to painting. But once I got my own little system worked out, I cut that time significantly! Waiting for the coats to dry is the most time-consuming part, which is why I paint two doors at a time.
There are lots of ways and techniques on how to paint doors out there, but I hope you'll find this one somewhat useful! Let me know how it works out for you!