I taught an electronics lab at the local college last spring, and two of the students were not able to get a decent solder connection. They were burning off the pads on the printed circuit board, and had large globs of solder on the few connections they made.
When they asked me why they could not get good solder joints, like the rest of the class, I asked them to show me the solder they were using. It was LEAD FREE solder that they purchased at the local Radio Shack. I gave them some 63/37 or 60/40 lead/tin flux core solder, and the joints from then on looked very good.
The electronic technicians at the employer I worked at, all cussed the lead free solder, saying they could not get decent joints with the stuff, and these guys soldered every day for years.
Flux cored solder is the easiest type of solder to work with, and less messy than having to use liquid or paste type flux with a separate dispenser.
Temperature control of the soldering iron is critical; it should get just hot enough to melt the solder you are using, and maintain the molten state while in contact with the work for three seconds. DO NOT leave the solder iron in contact with the work longer than three seconds, or you risk destroying the electronic component, and the pad on the printed circuit board.
The size of the tip on the soldering iron should be adjusted to fit the work; the larger the tip, the more heat it stores (and may transfer to the work). It is very bad to use a tip that is too small for the work; if the tip is too small, you will not be able to transfer enough heat in three seconds to complete a good joint - leaving the tip on for a longer time gets the work overheated, but not hot enough to melt the solder where it will flow and make a good joint.
When soldering, remove the solder from the joint before removing the tip of the soldering iron; do not allow the joint to move while it is cooling, or a cold joint may result. If the finished joint has a frosty appearance, it is a cold joint, and needs to be re-flowed with flux and solder. Components should be inserted in such a way that they will not move during the soldering process.