Solder adheres to what is hot. The surface you are soldering too has to be clean. Heat up what you want the solder to go on before you put solder anywhere. Once it's heated up, apply solder next to the tip of the iron. This should be used for most cases. When it comes to FETs, i put a small amount of solder on the iron to drag across the fet legs. If a surface is meant to be soldered, the solder should stick fairly easily.