Stick the sucker in there any old way. It actually doesn't matter a whole lot. An out of balanced prop is going to start moving no matter how it's "loaded" into that balancer.

Now, that said, to make the prop show its balance quicker, put it in horizontal. That way the heavy blade will have the most leverage to start heading downward, and you'll see it start sooner.

Also, after you start to gain experience, if you've always loaded the prop the same way every time, you'll be judging from the same starting point all the time.

BTW, if you're new at this, try to balance the worst prop first.

A prop that is perfectly balanced will not move from any load orientation. No heavy parts to start the movement.

And don't worry about bringing that out of balanced prop to that "no move" state. It's not worth the effort. It's a great learning experience, but not that important in practice.