that is easy as talk , but difficult at practice
so , you could use technical analysis supports and resistance
buy at support , sell at resistance
also , divide your trade to 3 phase (equal amount)
buy first time at first support
double your trade at second support ( preferred if the price get down to half price )
buy for third time at third support
so , if go up you can get out from this trade with your money ( its not to get profit , main thing to avoid loss)