Lisa's dead on (from someone who has moved a LOT),.
Job market
Cost of living
Schools
Area Stats
I would also throw in
Weather
Culture
Hobbies
Point A to point B
But those are enjoyment things. HUGE and need to be looked at but not first.
Job + Cost of living are the BIGGEST. 40k in some areas is solid middle class living, with a house, cars, and a couple vacations. In our area, that's below the poverty line. We'd live better in Illinoise making 40k than in Seattle making 100k. What you can afford will determine the neighborhood, schools, and your basic way of life.
My list of secondary items has been hard learned. Doesn't matter if you make buku bucks, big house, best schools... If every time you walk outside you want to shoot yourself because it's muggy, dry, hot, cold, pouring, stinks, too loud, too quiet, too dark, too bright. Doesn't matter if you're super extroverted and social if the culture is reserved, or if you just want some privacy, and people just keep showing up at your door. Doesn't matter if you're only 5miles to work and it takes you 2 hours to get there, or 20 miles to work and it takes you 20 minutes. Doesn't matter if you're 5 minutes to AmTrak if the only train through comes at 3am. Doesn't matter if you have 2 cars when you never drive them because trains run every 6 minutes, and parking your cars cost more than the payment on your house. If you live to hunt, but live in an anti hunting area, or live to ski and there are no mountains, or love to see music and there are no nearby venues...
To find a GOOD place, all of the above need to be met. To find a great place, they need to be met for everyone.