Kary, using a MIG, after I've jumped around with the initial tack welds, I'll planish those to stretch out what's shrunk up from the welding heat, then grind the weld dots down to just above the panel surface. (gets them out of the way for planishing the next ones) When ready for the next weld "dots", rather than centered between the last ones, I go to an overlap of the last dots. Then Lather, rinse, repeat. By overlapping it tends to eliminate the pin holes. Here's a post on a lower fender repair that shows it pretty well...
http://www.trifive.com/forums/showthread.php?t=9511 
