Buy low, Sell high. That's the only thing that works.
I usually trade everytime there is a $15 difference or more.
It is risky to trade when there is just a $15 difference as I used to do the same earlier and keep a $20 target. With the result, I lost a lot as when bitcoin price rises one day, it continues for just a day or two and then drops which makes me go in a loss. I keep a $30-$40 gap and when it's low or reaches this amount, I trade as then it earns me enough profit.