I have done Aluminum TIG welding, I taught myself, (I think I did one steel TIG weld), I can TIG weld aluminum better than steel, which isn't saying too much.
1. clean the surfaces very good
2. use stainless steel wire brush( and only use it for this purpose)
3. electrode distance from material should be 1/2 the electrode thickness
4. when the weld puddle turns reflective, start inserting filler rod (you can melt through very quickly wspesially with thinner metals, so this takes skill)
5. practice, practice practice
not 100% shure on #3, been a while.