How do you rig the spring line so you can grab it quickly on approach? I know that some people hang them off pilings, but some docks (mine, for example) don't have pilings in the appropriate location.
The easiest way it to have one left on the dock that is a different color from any other, so you can ask anyone who might be there to hand you the (red) line, or whatever color it is.
However, if no one is available, you take a long line and tie it off to the mid-ship cleat. Then take the line and make two small coils, one in each hand with about 4 feet of line between them, so that you can throw them over whatever you want to loop around on the dock. A cleat is great, but a piling, bollard, block or anything secure will do. Of course, when you throw the two coils, you must hold onto the untied bitter end so the line just loops over your target. You then pull the bitter end back to the appropriate length and tie right over top the first cleat hitch.
You never leave the boat and you have a line that runs from the boat to the dock and back to the boat. It is not a lasoo, you are only throwing a bunch of line behind whatever you want to catch and pull back against it. Takes about three practice tries for anyone to become a pro. Works every time.