Location, Location, Location. Visit the land at different times and days of the week. I even spent the night on mine in my pickup once. Location can determine future value, zoning restrictions, neighbors, crime rate, micro-weather, etc.... so it is not an easy decision and is personal.
Make your offer contingent on the perc test passing and other utilities readily available. This will give you time to do the dilligence necessary to discover the information. I had an obvious underground electric box within 600 feet of where I wanted to build and assumed I could use it but later discovered that it was 50,000 volts. I had to buy a transformer and have it installed by their "certified" installers... ended up costing $22,000 extra.