Speed of travel
The proper travel speed produces a weld bead with the desired contour (or "crown"), width and appearance. Adjust travel speed so that the arc stays within the leading one-third of the weld pool. Slow travel speeds produce a wide, convex bead with shallow penetration. Excessively high travel speeds also decrease penetration, create a narrower and/or highly crowned bead, and possibly undercuts.
A few last words of advice. Always remember that you need a good view of the weld puddle. Otherwise, you can't ensure you're welding in the joint, keeping the arc on the leading edge of the puddle and using the right amount of heat (you can actually see a puddle with too much heat roll out of the joint). For the best view, keep your head off to the side and out of the smoke so you can easily see the puddle.
Also remember that you learn through mistakes. There's no shame in grinding out bad welds. In fact, professional welders create perfect welds by recognizing imperfections, grinding them out and rewelding.