Turn continuation bets

[setjes]

I have a hard time figuring out when to make a continuation bet on the turn OOP (also with position, but less), and it may be one of my leaks. Does any of u have a plan for those situations?
Villain is unknown
Party Poker 5.00/10.00 Hold'em <font color="#0000FF">(5 handed)</font> link

Preflop: Hero is UTG with K[img]/images/graemlins/spade.gif[/img], T[img]/images/graemlins/diamond.gif[/img].
<font color="#CC3333">Hero raises</font>, CO calls, Button folds, SB folds, BB calls.

Flop: (6.40 SB) 6[img]/images/graemlins/heart.gif[/img], J[img]/images/graemlins/diamond.gif[/img], 2[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(3 players)</font>
BB checks, <font color="#CC3333">Hero bets</font>, CO calls, BB folds.

Turn: (4.20 BB) 9[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">Hero bets</font>, CO calls.

River: (6.20 BB) 4[img]/images/graemlins/spade.gif[/img] <font color="#0000FF">(2 players)</font>
Hero checks, <font color="#CC3333">CO bets</font>, Hero folds.

Final Pot: 7.20 BB.

So how would u play turn AND river if villain is a:
a) passive (peels alot, sees many showdowns)
b) aggro (raises many pairs on turn and is capable of folding)
c) maniac