Question on continuation bets

I did try to search for this, as I'm sure it's been discussed before, but not much there.

What percentage of the time do you c-bet? What boards/cards/situations should you not do it with? I have recently started to do it more often and it seems to be working pretty well.

And the big question: What if you c-bet with just overcards and get called? What's your turn action, both in position and OOP? This is the best example I could find, since I've only had PT for 2 days.

Villain is 58/14.6/0.58 over 50 hands.

Party Poker 50NL Hold'em, $0.50 BB (6 max, 6 handed) FTR converter on zerodivide.cx

Hero ($48.25)
CO ($48.32)
Button ($26.60)
SB ($31.65)
BB ($47.55)
UTG ($52.63)

Preflop: Hero is MP with A[img]/images/graemlins/heart.gif[/img], J[img]/images/graemlins/diamond.gif[/img]. SB posts a blind of $0.25.
<font color="#666666">1 fold</font>, <font color="#CC3333">Hero raises to $2</font>, <font color="#666666">2 folds</font>, SB (poster) calls $1.75, <font color="#666666">1 fold</font>.

Flop: ($4.50) 8[img]/images/graemlins/heart.gif[/img], 9[img]/images/graemlins/club.gif[/img], 9[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(2 players)</font>
SB checks, <font color="#CC3333">Hero bets $3</font>, SB calls $3.

Turn: ($10.50) 9[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(2 players)</font>
SB checks, Hero ???