1. Make sure said stairs have a lip at the front edge
2. Make sure you are in a hurry
3. Make sure you are carrying an armload of stuff (such as back volumes of journals or a bunch of gifts/packages/bags)
4. As you are going up the stairs, catch the tip of the toe of your shoe on the front lip of the stair
5. Fall forward (“up” the stairs), bashing your knee(s) into the stairs in the process
6. Two options: partial fall (6a) or full-on fall (6b)
6a. Don’t fully go down, just bash one knee, but manage to stop “falling up” by catching yourself, getting your other foot under you and onto the next step, and continuing up the stairs in a kind of half-run until you regain control
6b. Fully fall forward, bashing BOTH knees, spilling said armload of stuff all over the stairs and having to use your hands to stop your forward fall and to prevent your face from hitting the stairs. Compose yourself briefly by sitting on the stairs, then gather belongings and continue on, limping slightly.
You have now successfully fallen up a set of stairs.
For full effect, make sure to do this in front of a large number of people, preferably frantic and stressed out students during final exam time, or, alternately, frantic and stressed out shoppers with toddlers in tow the weekend before the Christmas holidays.