The rule of thumb I go with is "default to full names, use two-syllable given names only in very intimate situations, and never use one-syllable names on their own". That's what I osmosed, anyway, and what the previous fannish discussions have left me with.

ETA: Also, here's a bunch of links on name use (from the resource post):

https://twitter.com/oftenimprudent/status/1027305362335195137
https://naye.dreamwidth.org/2190770.html
https://naye.dreamwidth.org/2191577.html
http://foxghost.tumblr.com/post/178721212308/on-chinese-names