The first EMA (50) must be positioned above the second EMA (100). When this has occurred, it is essential to wait until the price comes back to the EMAs. In turn, the Stochastic Oscillator is exploited to cross over the 20 level from below. The moment you observe the three items arranged in the proper way, opening a long (buy) order may be an option.
Ultimately, each swing trader devises a plan and strategy that gives them an edge over many trades. This involves looking for trade setups that tend to lead to predictable movements in the asset's price. This isn't easy, and no strategy or setup works every time. With a favorable risk/reward, winning every time isn't required. The more favorable the risk/reward of a trading strategy, the fewer times it needs to win in order to produce an overall profit over many trades.