It's been awhile since I welded aluminum but if I remember correctly I would stick the whole tungsten out about 1/2" and switch the polarity to DC-positive and hold the torch vertical over a half inch thick piece of copper or bronze. And slowly ramp up the amps creating the ball on the end of the tungsten. You then have to slowly ramp down to prevent a crater or hole from forming on the tungsten ball, otherwise your arc will sometimes go directions you didn't want it to. Don't forget to switch back to AC.
I dont recommend grinding tungsten that has been dipped into the weld puddle. Instead hold the tungsten off the edge of a steel table at a slight angle and use a bronze hammer or whatever you got and break the contaminated tip off. An instructor from Miller taught me these things. If you do want to grind the tungsten use a grinding wheel that is only intended for aluminum. Use a separte wheel for other metals.
Use the largest gas lens you can find. It has wire mesh inside that allows the gas to flow better over the weld and also use Argon + Hydrogen for cleaner welds.
Also the key to good uniform welds is being relaxed. Resting your arm on a some thing that is propped up to keep your hand steady. This goes for your other hand that has the welding rod too.
Make sure your aluminum is preheated enough before starting the weld puddle. If you don't you get booger welds. Watch the joining aluminum pieces become wet looking and then apply some rod to form a puddle. Add the rod every second or two depending on your speed. And also remember to breathe. I use to hold my breath when I first began welding.
Adjust the tungsten so it is sticking about 1/8"- 3/16". When I was welding aluminum housings I would pull the tungsten out further and notice alittle more penetration of the welds.