I highly recommend reading "The Drunkard's Walk: How Randomness Rules Our Lives"

People perform worse than monkey while predicting random future events because they search patterns everywhere, they think they 'figured things out' and they choose less randomly which is not a good idea if you are betting on truly random event (such as raise or fall of stocks) since by not betting on outcomes mistakenly identified as unlikely reduces your chances.

Investment advice: 1. You can predict nothing so don't play short term and don't watch the stock market information, it doesn't help people that spent entire life trying to predict stock market even a bit so it won't help you but it will take a lot of time and will trash your emotions. 2. Buy whenever you have money. 3. Sell whenever you need money (and by need I mean REALLY need).

You may postpone buying a little bit if you see declining trend and loosen up a bit on 'really' in 'REALLY need' if you stock is currently worth much more than some time ago and tighten it up if you lost some money on your investments, but I am not sure if that does any good or harm.