Do you trust your GM?
It's a pretty straight forward question. If the answer is "no," then you should probably reconsider gaming with him. If the answer's "yes," well then "game on!"
At least is should be that simple. What about gaming at conventions? Or gaming with a GM out of some sense of loyalty? Or what if that particular GM is the only game in to town? What if the GM is a close friend?
Then things get tricky.
Victoria Praeparatio Amat (Victory Loves Preparation) is a series devoted to making gaming sessions great, the best they can be. Often what determines if a session is great or if it sucks happens before the players sit down at the table. Be prepared to have a great time.
As GM, I do enjoy putting my player's characters through harrowing experience, but the game itself should not be an harrowing experience for the character's player. You don't become a GM simply to tell and story, but watch what the players do--especially when they screw up. But you have to make sure when do screw up, its because of their actions, not because you screwed them over.
Screwing players over breaks the trust between players and GMs.
So what do I mean by "trust?"
In a nutshell, the GM will play fair for the players (not necessarily for the characters). The GM won't...
--show favoritism to a particular player.
--run a death trap scenario without telling the players beforehand.
--railroad a session to fit into a his story as an aspiring novelist.
--cheat against the players (some monster always seem to crit, some villains always seem to get away (etc).
If the GM has broken that trust in the past, it becomes harder for you to approach subsequent sessions without some lingering doubts. Such doubts can get in the way for a good time, and make a great time impossible.
If you have such doubts, it important that you bring them up before the session starts, preferably in private between you and the GM. You don't want things to boil over during a session. But if you're gaming among friends (remember, Be a Friend), then this shouldn't be much of a problem.
The same goes if you're playing a wargame with a referee or a boardgame at somebody's place.
Gaming at a convention, on the other hand, is a whole new ball game. The whole point of a convention is to try different things. Usually you'll know if you can trust the GM or not within 15 minutes of playing--believe me. You'll sense something--maybe he's not organized. Maybe his attention is off. Or maybe he can't get that evil grin off of his face. It all depends on the situation; conventions are an almost random assortment of individuals and experiences--box of chocolates and all that, with some of the chocolates stale.
The best thing you can do is be a friend.
If things get so bad, however, just walk away. You're time is fair more valuable that to spent it getting jerked around by a jerk GM.