Slowplaying is a tricky thing - helps to have position and a raised flop makes it a little easier too - as an example - just had a 55 set on a board of QT5 that was raised preflop with like 4-5 callers.
EP bets the pot on the flop...raiser folds - 1 limper prior to EP better had checked.
What does EP have? Depends on the player of course - not all that likely that he has KJ - probably just has the Q.
In this case, I was on the button so I flat called to slowplay (a little risky, and if I was in EP I would not have done this).
The player who checked the flop folded, so I'm relatively secure.
On the turn (a 3 - rainbow board) EP bets the pot again - like $4-5 at that point. He only had $4.50 left at that point, and I am now sure that he is on the Q (probably KQ or QT with that bet). I felt that he was pot committed so this is where I chose to go allin - and of course he called...river was a Q and I doubled up.

Just an example slowplay - not sure he's doing much more than calling reasonable bets if I raised much on the flop, so I am almost forced to slowplay to get max value. If other players had called before me on the button - no way I'm slowplaying any more - KJ/J9 has to pay to chase so I'm raising substantially - even if it takes the pot down right there I'm fine with it - I don't expect to double-up every time I hit a set.

So in general, as Fnord said - don't slowplay - at least not into very many folks. You just have to pick your spots based on the action and reads.