There is absolutely NO other method than buy low, sell high, there are only variations in how to do this, for example how to buy low and sell high since you can't really KNOW when there is a low or a high.

Juan... though in order to gain bitcoins at the end you need to accumulate more bitcoins on that side where you think the price will move (i assume one can short bitcoins too) so the bigger question is how do you determine if price will go up or down. I mean you can't blindly throw coins in both directions since that for sure will make you lose because of the trading fees.