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.
but you should be careful also in buying some altcoins. it doesn't mean that if see bitcoin price is falling down, you going to buy different altcoins. you should study first the coins that you want to buy or trade. because there are some altcoins that is very slow to move it's volume. always read a lot about trading or ask some strategy to those who are veterans in trading.