Originally Posted by Diseasel300

Adding to this advice, if you have a really NASTY looking joint, use some solder wick and remove the old solder, preheat the pad and pin well with the iron, then flow in some fresh solder. My go-to solder alloy is a 63/37 with No-Clean flux from Kester. The higher tin content makes it a harder joint than 60/40 and it tends to wick better. After soldering, clean the flux residue with some denatured alcohol and a toothbrush.