why is my welding inconsistent?

I started welding in a trunk pan and half of my welds look really good and the other half burn holes right through the sheet metal.....what up with that????:banghead:

No, I'm not concerned about settings and all that. I say that because I use the same 'technique' as far as I can tell, but sometimes I get burn through and, well for lack of a better term, I'm vexed as far as what is going on.