Whether doing it yourself or hiring someone, buy the best quality paint you can afford; it lasts longer and in some situations requires only one coat of paint instead of two. Painting a room usually involves prep work, primer and latex or alkyd paints with a range of finishes. HGTV.com gives a quick overview  as well as a list of painting dos and don'ts .
Pricing by the square foot for painting walls is typically between $1.75-$2.00 based on the floor plan, which equates to about $.55-.75/sq ft of overall wall space. So a 10x10 bedroom would typically cost between $175-$225 for the walls alone. Ceilings are generally between $.75-$1 a square foot, so another $75-$100, and trim should cost at least $1 a linear foot, but prices up to $3 a linear foot are pretty common, so trim for that 10x10 room would add between $75-$200. And doors should cost between $20-$50 per side.
"I had Sam and his team come in to repaint our kitchen cabinets that were originally a dark wood stain. He cleaned, sanded, primed, and put on 2 coats of sheer white on both the doors and frames of the cabinet and they came out great. The kitchen is much brighter and even up close it is hard to tell that the original cabinets were not white. They were prompt and very communicative over the phone. We may soon hire them back to paint the kitchen next."