One thing I prefer when getting feedback and therefore is a rule I impose on myself, is don't do this in the middle of a session. Further, as much as possible, bring up your concerns privately and not as some sort of 'Survivor' session where you are trying to organize the tribe against the GM.
If you don't like a ruling, think that the GM got the rules wrong, don't like where the campaign is going, think the GM said something jerky or hurtful, think the GM should do a better job at calling out bad behavior in another player, don't think you are getting your fair share of the spotlight, don't think that the GM is responding to your cues about where you want to go with your character, these are things to bring up after the session. Even the most sympathetic GM that is most open to criticism, is going to be a lot less empathetic if the player is derailing the game. No matter how reasonable your criticism is, if the GM gets the impression that you are the sort of player that enjoys arguing at the table more than they enjoy playing games, the discussion is going to get started on the wrong foot.
