I think you don't have to wait for the price of bitcoin to go lower. Because eventually the only way for bitcoin is up. It might dump sometime but it recovers again.
It would definitely go up but it's for long term. If you are aiming for some profit in a span of month or week then you must know when it is the good time to buy bitcoin. Bitcoin's price now is below 50% of it compared to December last year's price. So you just can't say to buy bitcoin whenever you like if you want to earn profit from it in short-term.