Forex traders usually find that their trading improves once they start to think about the outlook for currencies, and then afterwards decide which pairs to trade, instead of starting by looking at the pairs themselves.
For example, if a currency has been trending up against all its most important opposite currencies, it is probably going to be the best choice for a long trade. Another aspect of this kind of thinking lies in noting which currencies tend to move up or down together. As well as being a useful tool to use in knowing which currency pairs to avoid, when you see the pattern of correlation breaking down, it tells you something important about the market, and suggests a special weakness or strength in one or both the currencies.
For example, the British Pound and Euro have tended to move together, and have enjoyed a high positive rate of correlation. This made sense, with Britain’s membership of the European Union and its majority of trade taking place within the Eurozone indicating a de facto close economic union. Forex is about trade, about economic integration or the lack of it. The best trading opportunities come from trading currencies with divergent, rather than convergent, economies. 
Now the Britain is leaving the European Union by 2020, it may be that the correlation between the Euro and the Pound is coming to an end, or at least severely weakening. At present, the Pound is showing a lot of weakness. Earlier today, British Retail Sales data was more positive than expected, increasing by 0.6%, yet the Pound still fell. The GBP/USD currency pair has been unable to truly get established at long-term new highs, which we can label as above the psychologically important 1.3000 area, despite the long-term weakness of the USD. The Euro, in contrast, has continued to make new 1-year highs against the USD, and has been in a relatively strong and prolonged upwards trend over the past several months. At the time of writing, the European Central Bank is about to give its monthly “forward guidance”, and if they do not say anything which will have the effect of weakening the Euro, we can see an opportunity of divergence here which should be interesting to traders.