Although I've bought land, I'm not a specialist. This information is mostly second-hand.
1. To do it right, get the book Finding and Buying Your Place in the Country, by Les Scher. In addition to the money to buy the land, you need the money and time to have access to a car and spend months driving around looking at properties and looking up information about titles, water, easements, zoning laws, building codes, mineral rights, contracts, and so on and so on. Doing it right is too hard for most people to do alone. Better to buy with a group or find a shortcut. Still, at least look at Scher's book!
2. If you're going to buy with a group, choosing the members of that group is even more important than choosing the land. One energy vampire, one person who's contributing more money and demands more respect or decision-making power, one person who can't take criticism or won't compromise, even one person with a selfish and competitive view of reality, and your group is doomed. If you're lucky it will fall apart before you buy the land. I think one happy-dog person, friendly and easy-going but undisciplined, will add to a group, but two is too many. You need at least one person who's good at working out conflicts between the other people, and at least one person who's good with numbers.
3. The most common group-land-buying disaster goes like this: after a few years someone wants out, and wants to be paid their share of the land's current value -- but it's gone way up, and the other people don't have the money. So you have to sell your Eden to developers just so one asshole can make a profit. If you do not have a contract to prevent this, it's almost certain to happen. You must all agree in writing that if someone wants out, they get, at most, what they paid in.
4. Buy within your means. I strongly recommend you save up money and pay cash for the land. Loans are difficult to get, stressful, expensive, and multiply the things that can go wrong. Even if the seller will take gradual payment, it's more expensive and consumes psychic energy. Save up a bunch of money, set a maximum, and then push down from that maximum.
5. Think through what you want. For example, I wanted the following things: a) It has to be at the top of the watershed, or so close to the top that there's no risk of anyone putting shit or toxins in the water or draining it dry before it gets to me. b) There must be surface water on the land, a spring or stream, that runs at least part of the year. c) At least 5 acres, ideally 10, 20 would be a miracle at my price, which is... d) $8000-$15,000. e) Not too many north-facing slopes. f) Accessible by road, with an easement, which is a legal right to cross other people's property. g) The more remote, the better.
6. Think through what you don't care about. You get a better deal if you don't buy features you don't want. I didn't care about: a) View. b) Soil quality -- I can build it with composting. c) Natural beauty. I was all ready to get ugly depleted land and bring it back, though it turned out I didn't need to go that far to get in my price range.
7. Choose negatives! The way to get a really good deal is to think of features that lower the price that you don't care about, or even that you prefer, and actively look for those things! In my case, these were: a) No utilities. I want to be off the grid. b) No buildings. I want to build my own. c) Land that's just been logged. I preferred land that was naturally forested, but I knew I couldn't afford land that was actually covered with big trees, so logged land was ideal. I was willing to take a clearcut, but I was lucky enough to find land that had only been selectively logged.
8. Do not get "land fever". If you're overwhelmed with desire to just get on some land right now, you will not get a good deal. You can practice this just buying cheap stuff on ebay: the more patient you are, and the more auctions you are willing to lose, the better deal you will eventually get. Also, land fever tends to make you ignore red flags. A few years ago I almost bought into overpriced waterless land with a group that was young, undisciplined, likely to default on the payments, and already squabbling -- just because I was excited to pull the trigger and get on some land.
9. Don't fall in love. Unless you have more than $50,000, don't hold out for a piece of land that you are in love with, because you can't afford it. And don't fall in love with a piece you've seen, or refer to it as "my land" or "our land", until you actually own it. If you do, you are setting yourself up for the bait-and-switch, for ignoring red flags, for wishing yourself into a bad deal or a disaster.
10. Use your connections. Tell family, friends, friends of family, family of friends, and friends of friends, what you are looking for, and if you're lucky, someone will have a piece of land, or know of one, that is what you want. Then you can deal directly with the seller, who might be someone you know and trust, and you can cut out the real estate agent and a lot of precautions you would have to take with a stranger. This is how I got my land with almost no work -- my mom has a close friend who buys and sells primitive land. I was very lucky, but you might be even luckier, if your family has land that they're willing to give you free!
11. Before you start looking, research prices on the internet. It takes some time. The "multiple listing service" is some kind of giant database that you can supposedly search through any of a bunch of sites, but they are generally unusable and full of ads. I suggest you begin with a search for: multiple listing acreage, without quotes, and then the state you're looking in, and go from there.
12. The job of real estate agents is to lie. "Buyer's agents" and "seller's agents" all work for the same person: themselves, trying to sell property as quickly as possible for as much money as possible so they can rake in the commissions. If you ask for a low price, they will ridicule you for thinking you can find anything that cheap. But their own book of listings will have several properties that cheap! Then they will repeatedly try to seduce you into going higher, by showing you land that is above your price range but that you will fall in love with. They do this because it works on most people, so you have to be stronger than most people. They will also say, this land is about to sell so you have to hurry and buy now. It might be true, but the point is, they will always say it whether it's true or not, so it means nothing.
13. You can get a great deal by buying "problem" land, if you have the time and skills to solve the problem that scared off other buyers -- or if you don't care about it. Nothing lowers the price of land better, without being harmful, than junked cars.