I think mainly you have to look for patterns. I think there are some patterns with bitcoin for example like it will probably go down next year before the chinese new year and then go back up. It can be tricky to get the timing down perfectly but you can get extra returns if you sell near the top and buy back near the bottom. RIght now the pattern seems to be bitcoin is doing better than the alt currencies so that may be the best hold but that could end up switching soon.