The game moves more smoothly when, on a basic level, at least, the party gets along. In this context, I have three basic rules.
Your class will be known and accepted by all party members, even if you are a spell caster.
Within the party, a certain amount of mischief is expected. However, any attempts at turning on the party will backfire on your own character. The only exception I will make to this is if you're character's will has been influenced in some way (magically, psionically, or brainwashed). The judgement of when you've crossed the line will be mine and mine alone, but I will give you (one) fair warning. The following are some examples.
If, as a thief, you want to pilfer a few extra gold pieces from party treasure, I'll allow it (though at a higher difficulty class). If you want to steal the most valuable gem from party treasure or an item which is critical to the party in some way, I will not allow success, and I will impose consequences.
Also, you will not expose your fellow party members as spellcasters without their expressly given consent. Any such attempts will fail and backfire. If they do something stupid to expose themselves, that's an entirely different issue, and I'll let you roleplay your own reactions to that.
I don't mean to be draconic, but when characters become opportunistic at the expense of the party, it ruins the game as a whole. I (and others) have grown weary of playing in such campaigns, and I will not allow it in my world.
The point is for everyone to have fun, so let's play and let play.