Simplify the problem in your mind, and relax. Always have a boat hook close at hand before you enter the slip. Enter the slip slowly. (If you're going slow enough, you can grab a piling to stop the boat. If you're going too fast, you have to use the engine in reverse.) When you get your boat into the slip and stopped, it isn't going anywhere. The pilings hold it there. The boat has rub rails. It won't be hurt to gently bump the pilings. Walk forward (there's no hurry) and connect the spring line first. (I connect the spring line to a mid-ship cleat, rather than the bow.) The spring line will prevent the boat's bow from bumping into the dock. Then just walk to each corner of the boat and connect each remaining dock line. Connect the bow lines first. If you can't reach them, use the boat hook. When you leave the slip, always leave them in a way so that you will be able to hook them when you return.
If you visit a different marina, where your lines aren't already in place, put them on your cleats before you enter the slip, and follow the same procedure, attaching the spring line first.
If you visit a different marina, where your lines aren't already in place, put them on your cleats before you enter the slip, and follow the same procedure, attaching the spring line first.