Other than playing long, I think one has to have specific ranges of numbers in mind for exiting or buying in.  If you allow yourself to wonder how high or low it's going to go before you act, you might get caught.  For me the trick is to sell at a predefined profit you think is tidy, normally after a run up from an N.R. or rumour, and to buy in when you are happy with the increase in shares you'll accrue after the sp drops between N.R.s.  If the sp keeps dropping, you still have more shares than originally and when the price recovers, you have more money than you would have, keeping in mind I'm talking about good companies with good potential.