How much of the cigar tip should be cut?
The proper place to cut depends on the cigar. First you need to closely examine the head of the cigar. You are looking to see just how far the cap (this is the round of tobacco used to seal the head) extends down the barrel. On a parejo (a parallel-sided cigar) this is typically 1/4" – 3/8"; wherever the caps stops you should regard as your limit as to how far down you should cut.
The best cut is one above this "cap line" that will open up 75%-85% of the cigar's surface. You want as large an open cut as possible so as to allow for an easy draw, but you do not want to cut beneath the cap line as the cigar may start to unravel on you. Sometimes this means a thin cut of 1/32" is perfect, while other times you may need to cut 3/8" – it depends entirely on each cigar's construction.