Ive stripped the old paint using paint stripper.
I think this is a lot more efficient than sanding...(Ive tried)
I used my RSL membership card (which I dont use) to scrape off the paint.
TIP: apply a THICK layer and try to strip as much as you can using the chemical (sanding is not fun)
After stripping the old paint, I used 160,320, 1000 sandpapers to smooth the surface. (Never use a wire brush - its too tough on aluminium).
When the surface is smooth, give it a wipe using ethanol.