What I usually do if prices are falling most specially if the coins are very low, I would buy more coins from a much lower price and your total amount of couns would then be divided; the result would be lesser losses. Read or research on google about books or ebooks on trading.
I agree, basically it is the most effective in all trading business. You will buy when the price is low because it will save you a lot of money than buying in the time of much higher value. Also, you can invest more and more product when the price is low, so then when the price is higher your profit will be much more higher.