Paul__B:
The two gauges I have are actually 0.75 and 1.1 mm, and the finer is preferred.
As was mentioned... Clean is important. If something doesn't look bright-shiny clean it will be a -little- harder to solder. It'll still work but part of the job of the flux is to remove oxide. The drawback of keeping the heat on to burn through the oxide will, as seen in your video, much more easily melt the wire insulation. But common hobby wire insulation is such crap there's generally nothing you can do about it.
As was mentioned, yes, aim the solder where the iron touched the metal you're soldering. The iron heats the part(s), then you touch the solder in and as -that- heats up the rosin core melts and flows into the joint and does its cleaning job. Then the solder flows.
You pulled the iron away kind slow/gently. Try to pull it out as quickly as possible, with a bit of a snap-wipe along the wire. You don't want the iron to 'keep on heating' the joint - you want to get the heat away and let it start cooling as quickly as possible.
--- > And the real reason I'm replying to this... There are -two- important reasons you want to use an 'appropriately' sized solder. The larger stuff was too big because 1) the joint doesn't -need- that much solder, and 2) between the time you touch the solder to the joint, till it melts, it is actually sucking heat -out- of the joint. Yet, the wire/motor/whatever is still pulling heat -into- the part. The idea is to touch the the iron to the part, heat it up quickly, get the solder in quickly, and get the iron out. The intent is to avoid applying too much heat to the part. Typical Rat Shack connectors are HORRIBLE because you can't get the solder joint done before the whole plastic housing falls apart.