On April 26th, I learned a very valuable lesson during my very short time trading stocks.
If you want to be a winning investor, never short because you think:
1) the stock is overvalued or
2) because it went up too fast.
If you think a stock fits either 1 or 2, be patient, and wait until the market agrees with your point of view. Follow the stock and use technical analysis. When the the trend changes downward, then short it.
Remember that stocks go up at a slow pace, but it takes a split second to plunge; that is why shorting is an art and timing is everything.
Remember: shorting during earnings is gambling; Amazon (NASDAQ:AMZN) is an excellent example because the truth can be spun anyway one wants. The market isn't rational; it does what it wants. Sometimes you get so caught up in the emotions of trading that you forget that no matter how right you think you are and no matter how over-valued you think the stock is, the market is boss. Remember that.
Check out my other Article on Why Stock Options Are Bad