I find its best to start picking the snake fairly close to the neck. By the time you scoop it up, they snake will have probably moved forward and you will end up picking it up mid-body. This will prevent grabbing the poor thing by the tail as it tries to get away.
If it doesnt try to get away, just lift its neck up and then ease your other hand under the body to support it and pick it up. ALWAYS support the body in a coupld of places. They don't like to dangle. I saw someone get bit by a docile snake because they were dangling it by its tail. (can you blame it?).
You can reach in and let the snake smell you if it doesn't run away. But don't hesitate and jerk your hand back if the snake comes toward you. If you show fear the snake will be like "well he's scared about something, no way he's picking me up, CHOMP!"
If you grab the snake and it swings its head around it is probably just looking to see what's going on. Sometimes they will swing around and give you an open-mouth slap on the wrist. But rarely with a corn snake. Just remember that even if a corn snake bites you, it's not going to be any worse than some pin pricks.
Otherwise just let the snake do its thing and make sure it doesn't fall off your hand/arm. Don't try to touch it's head. It won't let you anyway.