Don't find a reason to keep a stock for tomorrow, that you wouldn't buy today. Do not worry about leaving money on the table. If your goal is met, that is all you should expect. Buy Just 12-20 Stocks. You must be able to follow the stocks you invest in, the more stocks you own, the harder it is to monitor what happens to each of them.
Diversification can limit losses, but it can also limit gains.
Look For Large Capitalization Stocks With Large And Growing Cash Flows. Most of the time, bigger IS better. Larger companies have more analysts following them and greater visibility, and are less likely to have trouble someone does not see. Be wary of One Product Companies. Things can change, do not put all your eggs in one basket.