I'll throw in my 2cents too. Make sure you don't spread the word that you are hunting Farmer Smith's land to everyone on God's green earth. Believe me, many farmers DO NOT like being talked about in a way that makes them look like they are being taken advantage of. If you get a YES, be happy and just hunt. Don't show-boat about it.
Also- DO NOT and I repeat DO NOT bring 15 of your buddies along for the ride. Most times when a farmer gives you the rights to hunt his property, it's for YOU and ONLY YOU... and maybe your son. That's it. If the farmer doesn't bring that up, assume the permission is for ONLY YOU, no one else.
Also last point... if you put up a stand for season, take it down after season- NO MATTER what the farmer says. Take it down and bring it home. By doing this, you are in a way, respecting that farmer's land- he has the right to tell you each and every year yes or no. By leaving your stands up you put him in an awkward position to allow you to do it every year. Remember it's truely a privledge.
Good luck to you