Skating down stairs on in-line skates is actually easier than it sounds. However, you have to commit to it, and if you fall, you could really take a tumble. Don't forget to wear your pads, especially while you're learning.
1. Approach the stairs at an angle with moderate speed, keeping in mind that the angle will depend on how much room you have to work with on the stairs. More angle makes it easier.
2. Remember that if you're going too slow, your wheels will catch on the stairs.
3. Crouch down low for balance and stagger your skates. The skate closer to the stairs as you approach should be slightly behind the other.
4. Remain crouched and hold your position as you go down the stairs at an angle.
5. Keep your weight over your skates and absorb the stairs with your knees.
6. Try to stay light on your feet as you go down the stairs.