Always have a chuckle when American's say the word soldering or solder, as the L becomes silent. In the UK we pronounce it "sowldering" and the W is to indicate that it sounds more like sow than saw.
Another way to solder them that is much faster is to do as Gus does with the 2 corners and then I apply tacky flux to the pins and then use a large tip with a ideally a concave face but a flat face one will do the job too. You then just flood solder along the edges on one continuous run. The flux helps to make sure the solder flows into the castellated pins. A quick spray with flux cleaner and you have a perfect soldered SOM. I used to do as Gus did but when hand soldering 10 boards it takes too long.
PS.. Have to add what cyberh0me said that focusing could be better