It is definitely about having the correct tool. Let's see, what do I use?
- Weller WMP micro pencil for tiny circuits and SMD stuff. probably have 6 different sizes and shapes of tips.
- Weller WSP temp controlled iron and an assortment of tips for routine electronic work. This is about the equivalent of GRJ's Hakko.
- Weller W60 temp controlled iron and tips for " heavy" electronics. Solders #12 wires with no trouble.
- Weller W200 temp controlled iron for huge wiring and light sheet metal work. Easily solders 1/4" copper tubing.
- Weller 140/100 watt iron, sort of overlaps the WSP and W60 but safer, heats up and cools down in a few seconds. Good for working under the layout or in tight areas; if you drop it it turns off instead of continuing to cook like an iron. Good for teaching kids, it turns off if they get distracted and leave it plugged in.
For general wiring on model railroad stuff I would recommend a good iron, like the GRJ's Hakko or my Weller WSP. Forget anything that is not temperature controlled, those are good for woodburning sets and not much else. First thing to learn is what a properly cleaned and tinned tip looks like, when brushed on a damp sponge the tip should look as if it were coated in mercury, all the way around. As far as solder goes, for a beginner, I would use something like Kester 44 50/50, rosin core, 062. 50/50 is more forgiving, it has a small plastic range during which it will tolerate SLIGHT motion. It also fills gaps better than 63/37, which melts instantly and has no plastic range. For the beginner, I would stay away from lead-free and silver-bearing solders, they are considerably fussier than 50/50 or 63/37.
One final point on the soldering process - All the "how-to" guides preach to high heaven about applying the solder to the work, and not to the iron. In my opinion that is seriously overstated and blind obedience to that rule causes a lot of frustration. Melted solder is a good conductor of heat, and a bit of melted solder on the PROPERLY TINNED iron transfers heat to the work quickly and effectively. As a point of fact, if the work is hot enough (and properly clean), it doesn't matter WHERE you apply the solder, it will flow by capillary action all over everything, including places you don't want it! But, if you have a red-hot iron, the loose tip black with corrosion, old oily wire and plumber's solder, the joint will never heat. Applying solder to the iron in this case will just make it melt and drip off, and unfortunately the fact that the solder melts at all is frequently mistaken for "soldering." Melted solder that "sorta drips" onto the wire won't work.
Start with correct tool, correct materials and a properly prepared tip. As a point of reference, soldering together two #18 wires, just a simple twist splice, should take 5 seconds MAXIMUM, typically maybe 2 or 3 seconds. If it takes longer than that, something is wrong!