I would start by finding out who owns it. Property records are generally open to the public and most areas have them available online. Check the local county site.
Once you know the owner, you need to find out where they live and ask if they want to sell. Determining the value will be another factor to consider. A great local agent may be able to do some research for you to see what other lots have gone for. Valuations based on the tax assessment, Trulia or Zillow are not reliable enough to make a financial decision on, so look at them to get a rough idea, don't trust them with your money.
Best of luck.