Thou shalt always retain focus
Given half a chance, other characters in the game (PC or NPC) will fail to really see your character. One of the hardest things in any roleplaying game is to make your character so much themselves that they can break through the preconceptions of others.
Imagine you wanted to play an idealistic philosopher. What would it take to convince an NPC that it wasn't a ploy, or that you weren't just covering for your weakness? At the very least, you would have to stick with your principles when it would be easier and more effective to do something else. That's what I mean when I talk about retaining focus. It's easy to roleplay your character when it is to their advantage. The trick is to keep roleplaying the character even when you know that it's going to cause them trouble. Especially when it's going to cause them trouble.
A friend of mine describes this as playing a character with "more attitude than sense". Me, I just think of it as letting the character's head serve their heart, rather than their heart serving their head. Either way, I believe it is what you have to do if you want to have each player playing a different character, rather than everybody playing the same slightly apathetic, self-interested person, with only surface differences. How people behave when the chips are down is, in my opinion, the true test of their character.
This is not to say that you need to always pick the most inconvenient possible way to express your character's personality. Doing that is just another way of making a Gag character, which I certainly don't approve. You don't want to retreat from your characters personality... and if being outright stupid is the only way you can think of to avoid that then that's what you should do. But if you can think of something clever that expresses their personality and gets you some benefit then that's even better still.