Flux? We don't use it for production as we are only permitted to use lead-free solders. If you MUST use flux then be sure to wash it all off thoroughly after the joint has cooled; use soapy water for acid-based flux and standard thinners for resin-based flux, applying with a stiff brush like an old toothbrush and working the solvent right into all the corners near the soldered joint. If you don't then the stuff will carry on slowly corroding the surface of the metal and eventually the joint will fail.
Both of my soldering stations are analogue temperature controlled. I use a old Union Brothers type from Maplins, fitted with a 3.5mm chisel tip for larger joints and tinning stranded cables.The other is a Weller which cost nearly £200 with the iron, but it is like a magic wand for smaller joints with a 1.2mm pointed tip.
It's the best maxim in the world that there's nothing which beats the right tool for the job. As for soldering guns, I wouldn't have one in the workshop. I found them clumsy and unwieldy to use, with a heat setting which can damage anything delicate in no time flat if you're not very careful.
Soldering electronics is easy if you remember a few basic rules:
Hold the workpiece steady while you solder. I find a good old bulldog clip is as useful as any fancy multi-clamp (which I have also tried and discarded). Wooden clothes pegs are useful for holding smaller components where you don't want the heat conducted away e.g. those Tamiya metal sockets and plugs. For repeat work we use jigs made from scrap MDF, ply and pasticard.
Make sure you have a good level of light and that you can see the joint clearly. If you need reading specs then wear them. I have a pair of 2.5x magnifying lenses which clip onto my standard specs and flip up and down as required - perfect!
Keep the tip of the iron clean at all times. A quick wipe of the tip across a damp sponge as you put the iron back into the stand, and again when you lift it out to use, should become automatic.
Use the right size tip. A pointed tip for tinning thick cable or soldering large components is a waste of time; you'll never get the joint hot enough. You should buy an iron with interchangeable tips to allow you to select the correct size for the job.
Use the right temperature for the solder used - this should be shown on the reel. Typically leaded solder will be around 270 degrees while lead-free is much higher (370).
Never carry solder to the joint on the iron tip. Tin the tip and use it to apply the heat to the joint, then tin the joint before bringing the components together.
Allow the joint to cool before you move it. This avoids dry joints.
On PCBs, clean off any surplus flux around the soldered joints with either isopropyl alcohol or meths; for lead-free stuff we have to use a proprietary brand of cleaner called Total Clean 200, but it's over a tenner a can!
Sorry if this sounds a bit like "my way or the highway" but I've done a fair bit of soldering over the last five years and this advice - for what it's worth - is born of that experience.
Like someone once said, suit yourselves.
Dave M