Whenver I ask permission to hunt on a place such as a lake cottage, I make sure I ask even up to six months prior to the season opening. When it gets close to season, you want to make sure you have the spot in the bag before another hunter gets that spot before you do. If your hunting for geese in a corn or wheatfield, usually it doesn't take much to ask the farmer for permission since they usually despise the bird that tears up their fields. Lastly, one thing that might help is asking the landowner if they would like to have some of the meat that you have shot. I have done this numerous times with the Omish who's fields we hunt. Make sure however, that you read the person, lets say if they dont hunt or really like the harvesting of animals but don't mind it, you may not want to ask them this. If they are a diehard hunter and you think that asking would be a good idea, well than asking this would help you in getting permission and keeping it in the long run. Also mention that you will pick up anything you drop (shells, feathers, wads, etc) and you will treat the spot with care.
"No bastard ever won a war by dying for his country.
He won it by making the other poor dumb bastard die for his country"-George S. Patton