What would I need to have done before the concrete is poured for the floor?

Have a drain, vent and trap arm already installed at least six inches below the slab and have a 12x12 buckout for the trap and waste and overflow.

Let me add a bit to the great answer growler gave you. The trap raiser should be centered 15 1/2" off the side wall and 1 1/2" off the front plate.
There! Now you have it all. Good luck, Tom