It's always difficult to tell the price actually, so i choose a particular price and make it a target price for both buy and sell, If the price gets there; fine if it doesn't i will wait until the price gets there, there is no need chasing for price rather set your own target price.
There are some traders out there that prefer to trade without a target price, basically if they open a position which has turned out to be incredibly profitable instead of selecting a target price at which they will sell, they simply let the market do its thing and keep moving up their stop loss if the price keeps increasing, now this is not a strategy that works well in ranging markets but when it comes to trending markets this strategy can be incredibly effective.