Good question! Knowing exactly when to buy and to sell is the essence of trading, and it’s as much art as science. Generally speaking, it makes sense to look for markets that you think are mis-pricing the chance of an event taking place or that are logically inconsistent (“inefficient”), i.e. the sum of all predictions is significantly above or below 100%.
Whatever you do, just make sure to manage your risk so that if you turn out to be wrong about a few things, you don’t end up losing more than you can afford.