I used the fine sandpaper to polish the deep scratches and cable rubs. Then you'll have ugly marks from the paper, so then you take the alu-polish and rub it gently with a cotton cloth.
Next step for the fine polish is a very soft cloth and rub it with a bit of alu-polish, the result is very shiny and smooth surface.
Just like SLIM said, for the large surfaces take the rag and "mailk maid" the tubes.
I did it the less subtile way. I used a alectronic sander, but instead of sandpaper I used a piece rag/cloth on it.
I didn't want to spend hours on polishing the whole frame, only the edges near the welds and the CNC parts I did by hand.