I don't ask for permission much anymore. Maybe from a few people I know. Back when I had the Brittany permission was almost a necessity if I wanted to get on some roosters. Back then I found it extremely helpful to have a plat book along. Onx will give the same info as the plat book.
When knocking on the doors I would always ask for the land owner by name and than introduce myself. It seemed most were surprised I knew thier names and most seemed to be put at ease. Not sure but maybe asking for the land owner by name shows you have put some due diligence into your effort and your not just a slob hunter.
Also look respectable. Wear decent clothes. Don't have the 5 o'clock shadow 3 days later. Be clean shaven or at least trimmed up nice and neat. If I were a land owner and somebody came to me looking for permission, His general appearance would play a big role as to whether not it was granted. If a guy shows up looking like Rambo after going at with the commies for a week chances are I m going to say move along. Not saying it's a fool proof method but it is a decent way to get your foot in the door.