I can go back to the way my father taught me plumbing. He would clean and tin each part of the fitting/tubeing, insert and then add solder.
When I was taught later by a machinist, the tinning was unnecessary. Cleaning, fluxing and cleaning after the joint is made is important. The rest is pretty much thermodynamics. Heating the more massive fitting first and letting the solder wick into the joint.
A good plumber can use MAPP gas without issues. He can make the joints much faster.
Later, a friend had a small plumbing project which involved a few water heaters. I taught him how to solder and I did only the critical joints or the ones that would be a real pain if they leaked.
He later completed a 40 fitting project and none leaked.
In the case of electronic soldering of lugs, you HAVE to make a mechanical contact first. Solder, basically without touching the solder to the iron and clean the flux off the joint after it is made. You do need adequate heat for a lug, so a temperature controlled iron helps. I would use my butane iron for this application.
"tinning" the tip and wiping with a damp rag is essential to get good thermal contact. DO NOT file the tip.