Make sure you have the space and money needed!
Projectors can be pretty expensive, especially if you want one of the newest models. Price can range anywhere from just under $1000 to well above $7500 or more.
Check around for deals.
Oftentimes it's possible to get last year's model for much cheaper than the newest one on the market. Check ebay or craigslist or AliExpress to get ideas about prices.
Know that all projectors work because they have a lamp inside of them.
Lamps can be pricey and in some cases hard to get. Before you pick a projector (especially if you are buying used), check to make sure that it's possible to get a replacement lamp. Again, these run the gamut from a few hundred dollars to almost $1000.
Check the price of the lamp for your projector and how much it costs. Also note that manufacturer's sell projectors with lamps installed. If you are told by a vendor that you must purchase a lamp separately for a new projector, buy elsewhere.
Lumens vs. contrast is usually the name of this game. Any projector over 1500 Lumens with a contrast ratio of 500:1 is typically going to work well in most settings.
Optimally, there should be very little light in your home theater room to interfere. As for resolution, MOST (but not all) projectors can display 720p/1080i.
Newer projectors can display at 1080p, but they are typically quite expensive. Check around and compare stats before you make a decision - there are a lot of factors to consider before you make your move.