Article in English: The more centered the stamp is inside the white perforation border, the better. You want the stamp to have an overall balanced, neat look. Stamp gum is the glue that sticks the stamp onto paper. You’ll want the gum to be as perfect as possible, with no skips or heavy creases. A stamp hinge is a small, transparent piece of folded paper coated in mild adhesive, sometimes glued on the back of a stamp and used to attach it to an album page. A stamp hinge will make the stamp-less valuable, even after it’s been removed. If your stamp has a stamp hinge attached, call a stamp dealer or expert before attempting to pull it off on your own, as you could damage the stamp further. Perforations are the small holes punched along the edges of a stamp that help you peel it away from the sheet. Some stamps will have more perforations or larger circles, but what matters most is that they have full teeth and clean holes. If a stamp has been used, it will be stamped with a cancellation mark over the design. The heavier the cancellation mark, the lower the value of your stamp; you want to make sure it doesn’t blot or cover the stamp’s design. You want your stamp’s design to be bright and vibrant. Fading color can be caused by things like sunlight or artificial light, dirt, pollution, or skin oils. Based on the centering of the stamp design and the heaviness of the cancellation mark, you’ll be able to get an idea of the stamp grade. There are a few possibilities for grade: poor, average, fine, very fine, and superb (mint condition).  Essentially, the worse the centering of the design and the heavier the cancellation mark on the stamp, the closer to a “poor” grade it will receive. Superb grades are quite rare, since the stamp must be perfect in all aspects. You don’t want to risk damaging the stamp by pulling it off or cutting it away. Sometimes an old, used stamp on an envelope with a special cancellation will have a higher value than the stamp would have unused and unattached. Ask an expert at a stamp show or get a professional...

Summary in Chinese:
判断邮票图案是否向中间对齐。 把邮票翻个面，查看背胶。 查看邮票胶纸。 查看齿孔是否齐整。 查看邮戳。 评估邮票的色泽。 确定邮票的品级。 要是邮票还贴在信封上，就保持原封不动。