1. You don't necessarily have to tighten up, but rather look for better spots. If you raise w/ AK in the SB and wiff the flop, you still should C-bet at least once. The chances with flat callers are that they have a small pair, and are set mining. With proper overs to their pocket pair, you should get away with a single c-bet. If they call and you miss the turn badly as well, just give up and check. If they check back and the river goes check-bet, you are most likely beat. Rarely in these occasions people bet as a bluff. Mostly it's for value.
Also, it all starts at table selection. I'm sure you are familiar with this, but I will re-iterate the importance of looking for opportunities before even sitting down at a particular table. If you have notes on anyone / someone is labelled as a fish - there's your chance. Remember, you are not looking to win every single pot, but rather get the most value out of those, which you do win.
2. C-betting really begs the question - what does the C-better hold, and does it make sense. With the previously mentioned AK example in the SB - if the board comes JT8 rainbow, you are actually a lot better off checking, as that flop is in his range way more as it is in yours (assuming you opened and he just flat called). There is nothing wrong with checking here. If he bets and gives you a right price, you still can continue to potentially improve to broadway. In short - just see, if your represented story makes sense (meanwhile try to estimate with what could he be doing the moves he's doing).
3. Oh, man... I have a serial betting problem (if Figaroo2 reads this, he'll have a laugh ). I just discovered that I need to quit doing this. It almost seems sometimes that when your image of a tight player is established, you should get away with nearly any 2-3 barrel bluff, but that just isn't the case. I guess the players don't pay that much attention at these stakes (I play NL5 myself) / they just don't care, but you only should double barrel (or even triple) when you are absolutely certain he will fold. There is nothing wrong with pulling off huge bluffs, but if this becomes a habit, it is very costly. Do NOT unconsciously just click that button. Again, think about what you represent / what he / she might have.
I'm just learning poker myself, but these are the ideas I could give out to you.