Get an idea of what the property is worth. You can contact the county recorder's office to get a list of properties in the area and find out what they sold for, or you can read the local newspapers; often the paper will list recent sales, prices and dates.
Contact a local real estate agent. The agent may be willing to give you a list of recent sales from the board of realtors if he or she is a member of the board. Be upfront: tell the agent you are interested in a parcel of land and you want to know how much it is worth.
Go to the county recorder's office or local escrow/title company and get information on liens recorded against the property.
Talk to property owners surrounding the parcel; they may have information the seller has not disclosed. If there is a problem with the parcel or area, neighboring owners are likely to know and very often are willing to share their information.
Go to the county planning department and see what the plans are for the area. Most counties have plans that extend several years into the future for development.
Write an offer on the land containing contingencies. Contingencies should allow for any inspection to be ordered - and paid for - by the buyer (you). Allow yourself enough time in the contract to get any desired inspections.
Make your offer subject to getting financing if you will be seeking a loan. Consider financing that will pay for both the purchase of the land and the construction of a residence.