My flagship trade for 2019 is the US 5/10 steepener. You have to buy ZF vs selling ZN. For those who are real traders and not paper trading, risk adjusted weighten between the March ZF and ZN contracts is 1,59 : 1. This means you need to buy 8 ZF vs selling 5 ZN.
As we are basically bullish for bonds in general, and technically we prefer buying 5y outright too, those who would like to run some outright risk may do so by selling Less 10y (ZN) futures against their 5y (ZF) longs. Me personally I do 2,66 : 1 ratio.