Elbow grease and steel wool are way more important than the polish. Best thing to do is start with a fine grade (0000) and be sure to lubricate it with water. I used an industrial grade acid but I also sprayed water to neutralize it after minimal rubbing. IMO, the wool is more important than the cleaning agent. Lots of scrubbing here is advised.
Rinse everything off thoroughly and then apply your polish. I tried both Meguairs mirror glaze (basically same stuff as NXT with a different label) and also the Eagle 1 polish wadding. I found Eagle 1 to be easier and faster to apply as its a liquid rather than a paste with better overall results. The Eagle 1 is great because you can use a microfiber to buff out the residue left behind where as the paste turns your microfiber or terry cloth towels black

It also costs about half the price of the NXT or P21S.
Best of luck and be sure to show pix!