It just takes practice. When you are driving look forward at the edge of your last pass of the cut edge and then look at the edge of your hood on that side. Figure out the distance between the two that gives you the optimum width of cut from your mower with only an inch or two of overlap. Memorize the distance between the two and use that to gauge your overlap. Try to keep your lines as straight as possible for a good finished look. If you make a mistake and your line has a curve or two, on your next pass compensate for it by overlapping a little more than usual. That is all there is to it. It takes practice and concentration to maintain a straight line. It is skill that is learned and you can spend a lifetime honing it. Good luck.