I think that managing distortion is a major skill in the craft of welding!
I was a total novice when I started. I was told by more experienced folk to tack everything up, check straightness and symmetry, then alternate my welds across the car. In other words, weld a joint on one side, then do the matching joint on the other side. This isn't a hard and fast rule - if I was welding up a T-joint in square tube I would do one side of the upright, then do its opposite side, so that it ended up at 90 degrees (ish), THEN I'd go to the other side of the car.
Basically though, don't go up one side and back down the other!
