Decide how you will finance your trading in advance: Only one kind of money is good for investing, and that's the kind that you are willing to lose, and preferably without damaging your physical and/or mental wellbeing in the process. Every profitable trader is profitable in their own way, while every loser experiences losses exactly the same way. Remember, use every available opportunity to learn. It's a never-ending process!
Imagine a trader who expects interest rates to rise in the U.S. compared to Australia while the exchange rate between the two currencies (AUD/USD) is 0.71 (it takes $0.71 USD to buy $1.00 AUD). The trader believes higher interest rates in the U.S. will increase demand for USD, and therefore the AUD/USD exchange rate will fall because it will require fewer, stronger USD to buy an AUD.
Diversify your portfolio: We all know the saying, 'don't put all your eggs in one basket', yet many new FX traders do this when it comes to their trading. Just as it isn't wise to put all of your funds into a single trade, relying on a single currency pair increases your level of risk, because if the pair moves in a different direction to what you expect, you could lose everything. Instead, consider opening a number of small trades across different Forex pairs.
By contrast, if you just traded 20 EUR, a loss would not significantly affect your account balance. It would provide you with the opportunity to learn from your experience and plan your next trade more effectively. With this in mind, limiting the capital you are prepared to risk to 5% of your account balance (or lower) will put you in a better position to continue trading Forex (and improving your technique) over the long term.