Buy bitcoin or crypto-asset when prices are low and sell when prices are high. However, if you want to get consistent profits when trading Bitcoin, then buy when "prices will rise, and sell when prices will fall".
Crypto assets trading can be considered a high-risk activity, where crypto assets prices are volatile, and can swing wildly, from day to day. Please do your own research (DYOR) before making the decision to invest in, or to sell crypto assets. INDODAX is not soliciting for users to buy or sell crypto assets as an investment or for profit. All crypto assets trading decisions should be made independently by the user.