When To Sell Winners
Professionals sell stocks only when the reasons they bought them are no longer valid. e.g a stock selected because it was undervalued is considered ripe for selling when it reaches "a reasonable valuation." Start with the stock's fundamentals, its P/E, P/S ratio, book value, and cash flow. Is it more expensive than its peers? If you're still the least bit bullish, it's probably too early to sell. The bottom line is that you have to always ask yourself why you bought a particular stock in the first place and if that reason is no longer valid, then it may be time to move on.
Another one : would you buy it again at this price? If answer is no, SELL!! and RUN!!
