I could add a few cold weather points from here in the North.
Overservicing can be an issue here. If an a/c spends the night at the gate in -30 the volume drops a bit. We have had some people service the system to full in the morning, Once the a/c and fluid is warm the expansion makes for an overserviced system. On the 737NG's we had instances of the overserviced system leaking and causing fumes in the air con system.
I would also add making sure the system is properly depresessurized before working on it. Both that the pumps are off and that head pressure is removed. I have seen many newbies think a system is depressurized when only the pumps are off.
Maybe a little point on lubricating "O" rings with a little fluid before installation in a hydraulic system could help a new guy out.
The possibility of cross contamination when servicing a/c from the same hydraulic container. I don't know about you guy's but here many 727 operator's supply 5 gallon buckets to service the system and these are used on all the a/c in the fleet. It could have contamination implications.
Hope some of this helps, good luck.