There is no better price to sell, because it is impossible to know how far it can go. What there is is good portfolio management. The only recommendation I can give you is that you try to divide your portfolio, even if you only have one asset (btc), and take the opportunity to sell on the ups and buy on the downs. For example, at current levels, it would not be bad to sell 10% -20% of the portfolio, and as long as it does not go down another 20% or 30% more, or go up another 20% or 30%, not to buy or sell again respectively.