Make sure you buy and use 63/37 tin/lead eutectic solder. It is the best solder alloy for hand soldering period. You live in the US, so you're not saddled with those terrible RoHS laws that might force you to use inferior lead-less solders for hand-soldering (leave lead-less solder to manufacturers).
The blend is eutectic, meaning it melts at a single temperature point rather than going through an intermediate plastic phase that can give you cold joints (brittle, low-strength connection from half-melted solder) if you don't pull away at the right time. The 60/40 blend is bad for hand-soldering, and for manufacturers that have precise control over temperature profiles and want a cheaper blend.
I also like having the wires held firmly to the diode leads before soldering (using helping hands), not holding wires to attach like what appears to go on in the video. If the wire moves during the cool-down it might result in a cold-joint.