The problem is especially fraught when writing about characters who already know each other well at the beginning of the story, or where all the description is being filtered through one character's perspective without the reader getting a clear idea of how others see that particular character.
I suspect that I don't describe characters enough for some people's taste, and sometimes fall back on comparatives that are in character, but may not be as easy to interpret for all readers. Mentioning that a character has a Glaswegian accent for example, only works if readers have some idea what a person from Glasgow might talk like. This is obviously compounded when writing in a non-contemporary setting. If a character in a futuristic setting affects an upper class accent most of the time, but slips into their more natural working class accent in certain situations, does it matter whether those accents are presumed to be the same as or different to what a contemporary reader would consider them to be?
'Compare and contrast' seems to be a useful trick. If our point of view character is focusing on what's different about the character(s) they're describing, does this tell us something about them as well? If a character notices that another character is white, does the fact of their noticing convey a different impression of them and/or their world than if the fact goes unmentioned? If a character notices similarities between the character they are describing and a third character, do we get a better idea about all three of them?
What tricks and descriptive shorthands do you use to get character descriptions across? How much do you like to know about a character, and to what extent to you prefer to fill in the blanks for yourself?