I’m sure this sounds odd, but how do you hop a yoyo? I can get into all the positions without hopping. However, it’s just not Kwijibo if you don’t hop it right?
Quickly pull your hands in opposite directions to tighten the segment the yoyo is sitting on. When you make this segment taught, the yoyo goes up into the air. 
Its hard to explain… You can do what gregP said, or just move your arms down, them shoot them up quick, you can try that.
Or do what both of the previous comments said simultaneously:
Pull hands in opposite directions while moving them upwards.
Thanks.
I learned it a special way.
The hop to cross arm thing I learned by doing a weird angled 1.5 mount. I would kinda hop it up and swiftly land in a 1.5 mount while rotating the whole thing around.