+1 on Ade's comments, I did some TIG at college years ago, got to the "aesthetic welds" stage with steel and stainless, aluminium was a fish of a different colour... A fish with very irregular scales.
Practice and more practice, and currents a bit higher than you'd expect, *thorough* cleaning - the higher the "cleaning" dialled in the more heat goes into the tungsten, so the bigger the tungsten needs to be, so the bigger the arc and weld pool.
If your welder "pulse frequency" works on AC as well as DC it's probably worth experimenting with - short pulses tend to spread the arc less, so concentrate the heat a bit more in the weld puddle. Some really posh TIGs let you set the AC arc frequency as well, same effect, higher frequency = narrower arc.
Dave H. (the other one)