When you're shopping for land, even if you're not planning to build now, check the conditions for building on the lot. Find out how the land is zoned. Is it residential? Industrial? Commercial? Don't get caught by surprise later.
The key thing is to ensure is that you will be able to get a building permit for the property and for the purpose you desire. Oftentimes, if a block of land is owned for agricultural purposes, you'll have to make the purchase conditional to the owner having the use of the land changed from agricultural into residential.
If you're purchasing land in order to build a house, make sure you invest some thought into what kind of house you want to build. Make sure the land matches up size-wise, has the right kind of soil and so on.