Are you primarily interested in using or investing?
I'm into using it as a currency, and I'm following the same strategy as you have been: I keep a little pocket money in BTC, but almost all of my wealth stays in USD. If value stabilizes I'll gradually let the BTC side grow by not bothering to trade back to USD, but that's a long way off. I don't consider the friendly side of the next bubble to be stable, and I won't be buying into it - again, I'm here for a transactional currency, not an investment.
If you want to invest... Well, that's a whole complicated game with even more strategies than there are players.
As for which exchange to use: Pick one located in your country (As I said about Exchb, they were in a convenient location for me to go burn their office down if they screwed me), owned by someone whose name you know, with fair T&C, and reasonable fees (about 1% round-trip is typical). Other than that and doing some background checking on them (read what's been said about them here), trust is subjective.