Nobody should tell you when to buy or when to sell, you have to figure it out yourself. There are some tips like buy when the price is low and sell when the price is high. The problem is how to decide if the price is high or low. Anyway, bitcoin is a little lower in price now, so maybe wait  if it decreases some more. But you could buy now, Bitcoin will go up eventually, that's for sure. Hold for a while till you think you have enough returns, then sell.