Judging by these questions themselves, I'd urge you to consider having them sprayed!

* Furniture-painting should be something you do if you're pretty experienced IMO. Many DIY-jobs just look like....
* Professional result come not so much from the paint itself, but the prep, techniques, and equipment!!
* Call around to some painters, cabinet-shops, or maybe even autobody-shops.
* Good prep to do ahead-of-time would include cleaning & a thorough scuff-sanding with ~100-grit paper.
* There is just no way to duplicate a good sprayed finish on GOOD furniture if you're a rookie.
* Priming, and possibly sanding a couple fully dried prime-coats with ~150 to 220-grit can be very helpful if finer finishes are desired.

>>> Clean & Dulled are crucial!!

What kind of pieces are they?
Are they daily-use?
My above points aren't as crucial if the pieces are just knock-around items in, say, a kids playroom, or casual outdoor chairs.

Faron

Ditto on everything the above poster aptly noted.

But to answer your question, use paint thinner with oil-based paint and water with latex. What type of furniture will you be refinishing/painting? If you are painting a piece that normally comes in contact with grease, use oil-based paint. Otherwise, latex is much easier to use and clean up afterward. I've done a number of pieces myself, including kitchen cabinets, dressers, tables/chairs, beds, desks, and bathroom vanities. Since spray-painting is better done by a professional (and costs $$$), I would recommend a high-quality paint brush if you choose to do the job yourself.

Here is a link that might be useful:

Hi, I cannot agree that you HAVE to thin the paint, I am painting the furniture all the time and I have never thinned the paint, unless I was creating white-wash effect on wood. Most important thing is to apply the primer first (water based before using water-based paints, and oil based before oil based paints). if there is uneven surface, you'll need to stripe the old paint using paint stripper or palm sander (or simply with a sheet of sand paper). After stripping, apply the primer, and when that's dry apply paint, no need to thin it out. You'll find that with some paints you'll need to apply 2 - 3 layers anyway to get even finish. Also let previous layer of paint dry completely before applying new one. It is also advisable to apply clear protective coat over the paint to prevent chipping, I recommend using clear beeswax polish, hope that helped!

Here is a link that might be useful: tips on applying beeswax polish on painted furniture

I think the quality of paint is equally as important.

I'm not a pro painter, but I painted my bathroom cabinets with a brush, 2 coats if I remember correctly, I didn't thin the paint and they turned out beautifully. Brush strokes should go with the grain of the wood. If using a darker color, you might want to consider a deep base primer.

When spraying, you want to thin the paint especially to prevent clogging the sprayer. There's a product called Floetrol you can purchase (orange bottle). I was told by the pros the ratio is 8 oz per 1 gallon of paint.