Can anyone help me how to know if the bitcoin price will decrease?
and how to trade bitcoins and earn? 
Because i invest bitcoins in yobit.net but i didn't know how to properly trade bitcoins. First, choose the coin you want to invest in. Watch the graph, it may pump or dump. If you think that the graph will pump, do a buy order(must be on the top). After you bought the coin, wait for the gaph to pump or sell it quick as you buy with higher price than the price you buy.