Here's the first row of pins by a beginning student. Note that the plating on this board is pretty minimal.
Problem: Incomplete solder joint on D, E.
Cause: not enough solder fed into the joint.
Solution: Feed enough solder to make a nice Hershey's Kiss shape.
Problem: Middle joint flows into adjoining through-hole.
Cause: Too much solder, or soldering iron crossing two holes.
Solution: Make sure your iron is firmly contacting just one hole/pin, and don't feed too much solder.
After just a couple of rows, the joints are good, and look like Hershey's Kisses.
Problem: "Mushroom" Top, no connection to through-hole. Look at the third from the right.
Cause: Not making contact between the through-hole and the soldering iron. The plating is pretty minimal -- this is more symptomatic of Cheap PC board construction. In our previous class we had some higher quality boards and didn't see this problem.
Solution: Bear down on the iron, to make sure there's a good concurrent touch between the pin and the through-hole.
And here's the same board, after cleanup. Textbook job! If you have a wedge or screwdriver tip, be sure the flat edge is touching both the pin and the pad.
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