The way I use/used one is to treat it like a lead, but longer ie. coil it up if Jack is near (sniffing/pooing) and let it out if he wants to wander a bit further. So they can be a bit of a faff compared to a normal length lead but it becomes second nature after a while. The important thing is to stop the moment he begins to pull at the full extent and encourage him back by your favourite method. You don't move off until the line is slack. Lots of encouragement/praise and the random tasty treat. The more you follow the routine, the quicker he'll get it. Eventually, when you're confident enough you should be able to drop the line and let it drag so you can step on it in an emergency but still have the now faultless recall... That's the theory anyway...
A long line is a godsend - and a good halfway house between being on lead and off lead. I prefer using one to a regular lead as it allows Jack a bit more freedom where he can't be off lead but can be easily shortened where more control is needed.