Well, first you need to know what the term of your strategy is.

Are you short term?  Then you need to figure out (good luck) where the market is going in the next month.  This is sometimes easy, but not always.  But if you are truly short-term, then you are playing with fire because of bitcoin's legendary volatility.

Are you medium term?  Then you need to figure out where bitcoin is going in the next 6 months.  This is a bit easier, since it tends to go in 6 month cycles.  And it's pretty easy to tell if you are at the peak or in a valley.  Check out Risto's (rpietila) and SlipperySlope's posts to see where we are at.

Are you long term?  HOLD.  Bitcoin is most likely not going anywhere with half a billion dollars recently invested around it, tax laws being created around it, etc.  You should definitely wait at least for the halving in 2016 and the release of all the ETF funds like Winkelvoss.  It's hard to imagine that bitcoin won't be at least $10,000 after all that is done.