Distressing jeans has been, and continues to be, one of the hottest trends in the market. While some jeans are ripped like crazy, more and more pairs look worn, but not destroyed. People will pay upwards of $100 to have jeans that have a worn look. It is possible, however, to make your own jeans with a worn look. It is incredibly simple, and can give you the fashion that you are looking for at a fraction of the cost.
Take the jeans that you want to give a "worn" look and put them on. Look at yourself in the mirror, and use the pencil or washable marker to mark out the areas that you would like to give the "worn" feel. If you are going for the general worn type, you want the most "wear" at the knees, with a general fade of the look above and below the knees.
After you have marked out where you would like the worn look, take the jeans off. This is a step in itself, as it is important to realize that trying to give jeans a worn look while wearing them is a bad decision.
Take the sandpaper that you have (the best and roughest you can find) and rub the spots on the jeans that you would like to look "worn". In the spots that you would like to look the most worn, rub harder and longer. If you want to fade the jeans out, rub less and less as you head toward the waist or ankle of the jeans. Rub until you see the desired effect.
Take the scissors or knife (whatever you prefer to work with) and rub the blade over various parts of the jeans. Focus on the pockets, seams of the jeans, and bottom of the jeans. Rubbing the blade over these spots will give a frayed look to the jeans. If you want a less worn look, only rub the blade over a few spots a handful of times. Again, rub until you see the desired effect.
Wash the jeans to get rid of the markings and to see the finished product, and make any extra adjustments that you need to.