2. New or used? Used bikes can save you lots of money, but can also give you lots of headaches. Like used cars, they bring with them all the abuse their old owner dished out. (This is a mountain bike, so there was definitely abuse.) Unless you know the history of the bike, buy new. There are some sweet deals on new bikes and they almost always come with a warranty and some kind of service package.
3. What's your budget? If you want dual suspension, plan to spend at least $1,500. Solid hardtails start at $1,000. From there, the price climbs all the way to the cost of a small car (can you say $10,000?).
4. With that info in your back pocket, try a few bikes on. Shop for frame fit and shock function—they cost the most to upgrade. Components, such as shifters, brakes and tires, can be swapped out pretty cheaply, especially before the bike leaves the store.
5. Take a few bikes for test rides. And keep an eye out for demo days. An actual trail ride is much better than a round-the-block spin. Many shops will let you demo bikes for a fee that they'll subtract from the purchase price. Ask yourself: Does the frame geometry feel comfortable? Can the bike do what I want it to do?
6. When you've made a final decision, get the shop mechanics to help customize the fit. They can quickly add spacers, change headsets and alter the seat angle to give you the most comfortable ride possible.