Great advice, it is a daunting process going up to someone you dont know and asking to shoot on their land, there's a lot of trust involved. The way i got mine was i noticed a field with a few rabbits on it, i found out who owned it and visited his home and just said who i was and that i noticed a few rabbits on his land i then offered to get rid of them for him, luckily he said yes and because of him i've got a few more permissions from his friends, it's all about getting your foot in the door.
Best of luck and dont worry if you are knocked back 20 times for every maybe its just the way i