Carefully toss the lure out, making sure it doesn't get caught in any other lines. This lure will travel down to the bow in the line. It usually will end up close to the midway point between the rod tip and the downrigger ball. I have run free sliders successfully on main lines set as shallow as 10 ft. They really work well in the spring when fish are scattered through the water column.
Summer is another good time as fish are scattered as the thermacline sets up.
I have run all plugs and spoons as sliders. When a fish strikes the free slider, the rod will really jump. The theory is that the fish will pull the slider down to the release and then pop up the main line. This does not always happen, so be ready. When the rod starts jumping, release it yourself and reel up the slack as fast as you can, then set the hook.