I've had fairly good success at this myself; just last week I secured permission to hunt one of the largest apple orchards in Illinois.

Rob hit on some of what I was going to say...

First off... I go in June or July at the latest. Hunting isn't as much on landowner's minds at that time, and they are prone to being more receptive. You'll separate yourself from the masses by not just being another of the herd.

I dress what's called "business casual" when I go knock on doors (pressed khakis or dress slacks and Polo-style shirt, nice dress shoes), and I usually go on Sunday afternoons. (Around 1:30 or so ... just after the family has finished their lunch upon getting home from church.) I don't drive my Jeep with the BOHNTR license plates and my sponsor's stickers on the side glass, either; I take the car. I haven't done it yet, but I plan on taking my wife along on trips of this sort in the future...

I STRESS that I am a bowhunter ONLY, and that I will NEVER bring a gun on to their property; that way, they never have to fear a stray bullet at any time (yes, I go ahead and explain that reasoning to them), and that I won't be on their property at all during gun season (because they may want to gun hunt themselves or have others in the family who do).

I offer to bring back some meat from what I kill off their land if they'd like some, and ask them what their favorite cuts are. I also offer to help with any work they may have lined up.

Thank them no matter what the answer is; you may want to come back and ask again next year. Offer up referals from area farmers. If you can't gain access on the farm you're trying for, ask if they know of any other property owners that may be willing to let someone bowhunt.

Follow up with a thank you card -- handwritten. In fact, I just got through mailing off all my thank-you cards to the landowners on whose properties I hunt; some of them have become so close over the years that I included a recent pic of my two boys along with it.