I do used to buy coins when the price is fell back ward and there is a serious dumb. The coins must have fell back world to said 30% and sell when it is in positive of 10%. I have never make a serious loses but make a reasonable profit. I have decided to follow this ageing principle of buying low and sell high.
I also to that. I buy coins when the price is low and I sell it when the price is high. This is the simplest way to to earn money. Having also a knowledge to all of the coins is really important. It can help you to make a wise decision.