Black to move. What would you play?

I came across this position in a recent game that I played.  I was Black, and although I ended up winning this game, I tend to think my choice of move was incorrect.  I wanted to start my attack on the king so I played b5.  I thought maybe there was an in between move or two before going after the king.  What do you think?  Would you play b5 or would you play something else?