The front and stern lines should extend from the boat at a roughly 45° angle. You shouldn’t use the center line for mooring because it tilts the boat, but for mooring while waiting at a lock while the boat is otherwise attended, it’s OK.
To leave a mooring, someone can push off the front of the boat and step back onboard once the boat is moving. It doesn’t take much to move the boat away from the towpath or bank unless there’s a wind or other current keeping the boat there.
Leaving a tight mooring
Often you’ll need to leave a mooring when there are boats in front of and behind yours. If you don’t have someone to push off the bow, then swing out the stern of the boat by pointing the tiller sharply away from the bank and apply forward throttle. Once the stern is clear of the boat behind you, apply reverse throttle until you have room to maneuver the front of the boat.