When using the open end of the wrench to its most benefit you will want to put it around the nut or bolt that you need to turn and twist the wrench in a counter clockwise direction. If (and when) the nut gives you a difficult time I normally give it a good soaking of penetrating oil. Then shortly after applying the oil, I'll tap on the head of the bolt, or the side of the nut to help break the tension on the threads and let the oil work into them a little deeper than it would otherwise.

    Always try to use your free hand to secure the wrench down over the nut. I do this to control the wrench to a greater extent and prevent it from coming off and damaging the nut or something else, such as myself.

    In tight places sometimes you can't move the wrench all that far. The opening it typically at a 15 degree angle so that in those situations you can turn the wrench slightly and then flip it over to turn the wrench another 15 degrees so that you don't need to reposition it.

     Never, ever think a wrench is "tight enough." If there is any play at all between the nut on the wrench, don't use it and find the proper size wrench. If it was too big and slips off the nut, it can easily round off the corners or the nut and round the wrenches of the wrench. There's no point in destroying a nut or bolt and your tool when a few seconds to find the right wrench is all you need.