Buy low sell high works across every market. If you buy dips, you end up with a larger amount of whatever coin you're buying than if you would have bought at the initial price. It's simple economics.
The way to keep your eyes peeled for this information is to frequent exchange sites, keep the buy/sell orders in mind, and most importantly keep up with news about the markets. If you see some bad news, you know the prices will drop and likely rebound. You can buy when the markets are low. If you see good news, you can opt in again, since you know the prices will go up, or just sell what you bought at the low points.
So, holding and selling need to be combined in order to create a true full trading strategy in my opinion.