There's no set strategy, but it's always a sensible move to ladder out your profits. I tend to sell at least 50% of my holding if it goes up 20%, then gradually sell out until I am holding only 10% in case it has a huge jump. If a particular coin has a 100% or more rise in a very short space of time, I will sell 90%, as generally it will drop sharply afterwards, giving the opportunity to get back in if I want to. If it doesn't drop, then I'm (normally) happy enough with the profit and move on to the next one.