You shouldn't slowplay hands like two pairs, sets, straights and baby flushes. Wrong card hits the board and your opponent beats you, then you realize what mistake it was.
Yesterday though, I was in a 3-way pot with AJs and flop the nut flush. I still have to c-bet because an opponent has position on me and it will be hard fir me to extract any value if I check the flop and bet the turn. Ok, so I bet 1/3 and he min raises. At which point 3-betting is probably not an option, so I call. The turn is an 8, blank. I check and he second barrels quite a large chunk of his stack. Now, I'm positive that he has a decent hand and since I'm OOP I should check-raise him. He 3-bets the rest of his stack and flips over a two pair (Q8)
In general though, you shouldn't be slowplaying all that much unless you flop Quads or the high end of a fullhouse.