Position your tip where there's the greatest thermal mass, otherwise you risk overheating the area your tip is placed because of poor heat transference.For instance, place the solder tip on the same side that the trace intersects the joint.
An incorrect placement can also lead to a cold solder joint or risk over heating your components particularly if you solder tip is in contact for more than three seconds. the general rule follows the greater the mass, the greater the temperature requirement,though their are always exceptions.
Also do not let the soldier contact the joint until you notice that the existing solder has melted. Again, no more than three seconds or you have misplaced your tip or are using too low a temperature. The entire process of heating, solder contact and cool down should take no longer than 5 seconds. I have known many experienced fabricators that could complete the entire process in many instances in just a couple of seconds.
There are of course many variable and exceptions when practicing this art or skill.
This is the best I can do at 5am and it's been well over a decade since I taught NHB solder.