Stairs are the job most people leave until last. Carrying a heavy vacuum and bending over every step is hard work.
Go handheld
Take the wand off and use the vacuum as a handheld. You carry less weight and keep it close to your body.
Start at the top
Work down one step at a time so dust falls onto steps you haven't done yet.
Tread first, then the edges
Do the flat part of each step, then run the crevice tool along the back edge where dust collects.
Stand to the side
Keep your back straight and stand beside the step, not over it.