I've been playing casually since beta and always soloq so I'm hardstuck in bronze (I don't belong anywhere above silver so it's okay). Therefore I'm continually matchmade with newer players. I'm always understanding, don't comment on first mistakes and try to be positive. When I do comment it's usually:

"Please shift at the beginning of the rounds, you're giving away our position right away"

"Please put smokes on their positions, not where we are / don't let them run up to us / put it here [pings on map]"

"Please don't peek"

"Please keep eyes / camp on spike"etc.

I never backseat, I never call anyone names or anything like that. 99% of the times I'm being labeled as toxic and insulted, no matter if comp or unrated. Last comp match my mate literally sabotaged me for asking him to not put smoke on me. He kept getting me killed with smoke and paranoia on purpose. It's really, really demoralizing. Please understand that it's not meant to ridicule you or something else negative, it's a team shooter and I'm trying to help my mates.