The first step involved in preparing a cigar for use is to open a passage way allowing air to circulate from one end to the other. Some smokers elect to bite the tip off the cigar; its quick and easy solution and there is no need to carry around any tools. Most cigar connoisseurs however use a specialized clipper that provide a clean, manicured cut.
If a cutter is used, the incision should be made quickly and decisively. The cutter should be placed just above the cigar's cap line (the curved area that covers the head of the cigar) and clipped in one swift motion. This produces a clean cut which is desirable for smoking a cigar.
Credit: CigarHandbook.com - Your Guide to Cigar Smoking