I've bought land, held it a year or less and sold it for nice profits. One of the people I sold land to 4 yrs ago still has a 4 sale sign sitting on it and likely will for awhile due to the economy and his ridiculous asking price. I am far from an expert on land investments but can share with you the little I know from my limited experience.
I found that making friends or business aquaintance with a realtor that also develops land is helpful. If you can get in on the ground floor it makes a big difference in the profit and the quality of the lot. I focused on lake view/front areas exclusively as they are always a premium. I pay to have the land cleared to allow the prospective buyer the best view of and from the lot, and I price it reasonably well because every year you hold it, taxes eat away at your profit margin.
For sale by owners can be a good find. Some owners around lake areas bought land and moved away.. just riding around the area you like could net you a good find that isn't listed. Another thing you can do that I have done before is even if a lot doesn't have a sign, but has been vacant for a long time, you can do a property search to locate the owner and make an offer, all they can do is say no.
