When you know that the price is fluctuating and going more in the forward ratio then you can set your coins for selling in order to earn profit and if the ration of downward sign is going more than you have to decide more to buy the Bitcoins or any coins you have but Bitcoin is the most responsive ones in the market. When you have a lot of money then put forward for Bitcoin and if not a lot of money then start trading and make money in order to step forward for investment.