How to diversify your portfolio in order to decrease risk of ruin
Taking in consideration that a black swan event will happen somewhere in time and brokers will "margin call" you , what do you do to mitigate that risk ?
In practice, how do you diversify your portfolio ?
What are the best instruments to balance positions in EUR/USD and other majors ?
Keep your holdings as diversified as possible. Ideally, you'll want to try to keep the absolute correlation of your trades as close to 0 as possible. As Armil has pointed out, having a set of diversified trading strategies based around different market conditions is also key.
Some forex pairs that are most uncorrelated to EURUSD would be AUDCAD, EURJPY, EURCAD, EURAUD, CHFJPY, and CADJPY.
In my mind the best way to diversify is not by markets, but by strategies and position sizing.
There is a difference between worrying about risk of ruin (which I think is healthy) but being scared of risk is something else. You might need to have a look at why you are scared of uncertainty... if that is the case.
Taking risk all depends on your appetite for risk.