Flux core solder is crap. It doesn’t contain enough flux to begin with and since it’s inside the solder, it can’t actually do the work it’s supposed to. You need to apply flux separately before soldering, and lead-free solder used to be harder to work with. That’s the leading mistake I’ve seen frustrate beginners.

Steady hands aren’t a requirement unless you’re doing very complex repairs like threading wire through a BGA grid. You’re supposed to use the surface tension of the solder to snap the component’s pins to the PCB pads. After you snap two corners to the pads, you can just glide a tip with some solder over the rest of the pins and the heat and flux do the rest of the work (the flux’s main job is actually changing the solder’s surface tension to make this easier and more predictable).

Thermal mass is important, please have a look at my other post for a recommended tutorial set. Silver based solders like SAC305 will also stick to most plated pin types.

Sometimes people are given a BS fools errand, and convince themselves there is some hidden secret to workmanship. You would have been better off with a $25 30W Weller iron and $7 flux+Wick kit off Amazon for through-hole style PCB kits. =3