There are also a few tools which are necessary to do the job well. It is up to you to try these and see which works best. You effect the strength of the soldered joint by the amount of lead or tin content. Over time, the tin will crystalize weakening the joint. Tin, more than lead, is effected by a wide variety of chemicals.
Temperature can also have a detrimental effect on the adhesion of tin to the joined surfaces.
As you have probably seen, some joints just seem to come apart for no reason. Usually this is due to an unclean joint but can also be attributed to high tin content in the solder. In the US there is a movement afoot to eliminate all lead solders due to a general hysteria over lead exposure. Because of this, solder manufactures have come up with a new solder using a low temperature silver. I have this in the shop and use it periodically to get used to it.