We all make mistakes, especially when trying something new. Soldering is no exception, so here's what to do when one of your soldered joints comes out less than ideal.
Lay a strand of desoldering braid over the solder in question. Press the tip of the soldering iron firmly onto the desoldering braid. This will heat up both the solder and the braid.
The solder should flow from the joint to the desoldering braid. After the solder flows into the braid, remove it and the soldering iron from the board. You should now have a clean contact to start over with. Use wire cutters to cut off the used end of the desoldering braid.