The only tip for aluminum welding or cutting is go hot and fast, as fast as you can go, and no oxygen.
Your cuts look pretty good to me for air plasma. I have never seen super smooth cutting with air shielded plasma before, always is a bit rough and gritty looking. Its caused from the excess oxygen in the air plasma creating the tough protective oxide layer on the aluminum at random as the fresh aluminum is exposed by the plasma arc.
The only clean"er" cuts with aluminum and plasma use inert shield gas or inert shield gas in conjunction with submergence.
edit aluminum safety…
The guys at ESAB have a good bulletin, should not effect us as much due to our tables size. But some aluminum alloys are an explosion hazard.
http://www.esabna.com/us/en/education/blog/can-you-plasma-cut-aluminum-on-a-water-table.cfm