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. The price of bitcoin is very unpredictable. Also not all member in this forum is not psychic that can predict it actually. But you can do trade anytime you want. Aside from that for you to know the proper way of trading just observe the traders in the different exchange platform.