Free: Contests & Raffles.
Asking early is definitely key, but then you need to keep in touch. I don't know how many times I have recieved permission only for the landowner to subtly back out when the season comes around. Try and have specific dates in mind and tell the landowner you will be taking vacation from work or something. This can make him feel more committed to letting you hunt. I've been pretty frustrated lately with flaky landowners. Another option is to help him out with chores after you recieved permission, whatever makes that person feel committed to holding up their end of the deal!
my hunting group has hunted the same property for 25 years or so and each year we make sure to help the landowner out with computer issues. she has something new each year for us to teach her, or fix for her and we get it done. we also stop in and chat for a few minutes here and there when we see them at the house or at the barn. being personable and working toward getting more on the friend level rather than just some person that is hunting their land is very important.