Buy low sell high.
Yeah sometimes this strategy was successful. but what if after the price drops and we bought, but prices continue to fall? what would you do ?
You gotta use an efficient stop loss system in order to be safe from sudden downfalls. There are some automated bots that will trade for you.
Trading, though, is only worth the trouble for significant amounts of invested capital. And the risk is, of course, much bigger than just hold.