Whether you are a beginner trader or a pro, it is best to trade with what you see and not what you think. For example, you might think that the US dollar is overvalued and has been overvalued for too long. Naturally, you will want to short and you might be right eventually. But if the price is moving up, it does not matter what you think. In fact, it doesn't matter what anybody thinks – the price is moving up and you should be trading with the trend.
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!
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.