This is the end of the cigar that goes in your mouth and is called the head of a cigar. The opposite end of the cigar is known as the foot. The head is distinguishable by the fact that it has a cap on it, a round piece of tobacco that is stuck onto the head in order to keep the wrapper of the cigar together. The head is also usually easily distinguishable because it's the end closest to the logo sticker wrapped around the cigar. The shoulder is where the curved end of the cigar starts to straighten out. Right above the shoulder, where the curve is still intact, is where you'll you want to cut.  Line it up so that you're cutting right above the shoulder of the cigar. Remember that it's better to cut too little than too much. You can always go back and cut more cigar off, but it's impossible to go back and put already-cut cigar back on. Better to be safe than sorry. Keep a tight grip on the cigar with your other hand and try not to let it move until it is cut all the way through.  Quickness is key here. You want the guillotine to slice through the cigar quickly, not tear through it slowly. Make sure to grab a sharp cutter. Like a kitchen knife, the sharper your guillotine the better. Unless disaster strikes (it won't), you'll never regret having a sharper implement.

How would you rephrase that briefly using Vietnamese?
Chọn đúng đầu của điếu xì gà để cắt. Nhận biết phần “vai” của điếu xì gà. Kẹp dụng cụ cắt xì gà bằng ngón tay cái và ngón tay trỏ, sử dụng tay thuận của bạn. Đặt đầu điếu xì gà vào dụng cụ cắt, nheo một mắt và nhắm thẳng điếu xì gà một cách chính xác. Cắt xì gà một cách dứt khoát bằng một thao tác gọn nhẹ dùng sức ở ngón tay.