Buy low sell high is the basic knowledge you should have and understand, with out that loss will be yours all the time. If you're already trade for long time I believe instinct will become the main decision. People can learn in many ways with different performance but trade basic knowledge is the same and practice ( only ) the best way to increase skill. Last thing is if want to become successful trader, never repeat the mistakes.
If this would work everytime we would have many rich people because of trading. Sadly sometimes when you buy currency that looks cheap, it crashes even more without any hope to recover to the last price which leads to losing money.