How to paint Unpainted Furniture?

Quite often, in speaking with people, I'm left with the sense that many feel that painting bare wood furniture must be a difficult process. Rest assured that it is not. As with most any job, preparation is the key, and with proper preparation, your end result will be everything you're hoping for.
The first question that needs to be addressed is the why? Why are you painting the piece in question? If the piece is constructed of a softwood then it often makes sense, as the wood can be seen as somewhat less attractive than some other types, and a hint of color can be just the thing to draw out the full beauty of the piece. There are paints, stains and dyes available in a multitude of colors, so you'll certainly have no trouble finding just the one that suits your personal style and specific decorating needs.
The first thing to do with the furniture then, is to prep it for painting. Most often, this means sanding. You'll want to use a fine grit paper, and be sure to wipe the piece down well before painting. Make sure to apply sealant to any knots and/or cracks, then prime the piece before applying the paint. If you don't, it might crack and peel off.
There are a variety of different paints available, but the majority of folks seem to be opting for water-based acrylics because they dry fast and are easy to clean, and generally easier on the environment. If you're painting a piece for the kids' room, be sure that whatever materials you use are suitable for children, as they DO have a habit of putting things in their mouths, and many aren't above attempting to taste test the new furnishings!

If you've bought a piece of unfinished oak furniture, then you may want to think twice before painting it. Oak is a beautiful, natural wood, and a simple wax or stain finish might be more appropriate, and serve to highlight its natural beauty. You can always use a tinted wax if you want to subtly alter the hue of the finished piece.

If you've purchased a piece of unfinished furniture for outdoor use, this changes the equation somewhat, and you'll need to use a preservative to both stain and protect the piece.