Soldering is actually both a skill and an art. We each tend to develop our own techniques and eventually favor a specific type of solder. I don't use a temperature gauge on my iron, I just find the setting, (thru trial and error), where I can get the iron tip on and off a solder point in well under 10 seconds. I've got it down to a point now where I can get the iron tip on and off in ~3 seconds. If I exceed 5 seconds, I back off and wait for the solder point to cool and try again.
And the on/off timing is different for different components. For wiring points, LEDs, photo-couplers, resistors, 'box film'/MLCC/polyester/ceramic & most electrolytic caps, chips/sockets and small transistors I adhere to a 5 second rule. For larger devices/components like pots, reverb bricks, larger transistors (TO-220, etc), switches, and the like, I adhere to the 10 second rule.
Lower tip temps can fool one by melting the solder - but not heating the entire solder connection point enough to allow the solder to easily flow. This can lead to over-heated PCB pads, often-times causing them (the PCB solder pads) to lift/separate.
Higher tip temps can trick us when we leave the tip on the solder point too long and burns the joint that way.
It takes practice and patience. There is also a relationship between the technique and the type of solder being used.
I learned how to solder from the older NASA Soldering Guide. Here is an updated PDF version of that earlier
NASA Student Workbook for Hand Soldering. And here's another
NASA Soldering Guide. It has some great photo examples. I hope they help.