The main things to remember in learning how to mig weld overhead are...
1. Set the machine hot...just like you would for welding flat, right on the workbench in front of you...This takes advantage of the arc force of the mig arc... setting it hot will make the weld flatten out instead of piling up....IF...you keep the stickout short....voltage and wire speed should be set the same as you would weld for flat or horizontal welding.
2. Keep your stickout short. In order to to this, you are going to have to make sure the contact tip is flush or even protruding a bit past the nozzle. When you weld overhead, you will always have a longer stickout than you think...so you have to compensate by making sure your contact tip is not recessed at all.
3. push or pull ...either one works but realize you will get more spatter pushing and dont get all crazy with gun angle either way.
4. A series of cursive E's will make a good looking overhead welds....its not the only way to do it, but it sure works.
5. Use both hands when possible. If you are lying on a creeper and under a race car...and you can barely reach the weld with one hand, do what you gotta do. But as a rule, both hands are better than one.
6. Learning how to mig weld overhead is just like learning how to mig flat...its just upside down.
"I bought a tig finger and love it! I use flux core and it works perfect on the finger to cradle the neck on my gun. No more red fingers and smoky gloves. "