first off you need help from a friend or willing partner.
It sounds like your kit has been fitted before so I would put together the screen and supports.
I would then hold this in position on the scuttle and offer up each of the doors.
once you are happy that the doors will clear the rear wings and fit correctly then you have your screen position.
Make a note of what angle the screen is at and take measurements from the top of the screen to the roll bar at a few marked points.
This will ensure that the doors don't rub the wings like mine do at the moment
It is hard to say how to fit the hood without knowing how it attaches to the screen. Mine had a bow which the hood was glued to so I had room to play a little.
Assuming yours has been fitted and I would guess with poppers I would in your case fit the hood to the screen and get a rough idea of where the poppers will need to go on the rear tub.
Now to keep every thing nice and tight you will want the air around and the hood itself to be nice and warm, this will make it more plyable and easier to fit also when the hood cools it will get tighter and when its sunny it wont sag as much.
If yours is allready fitted with poppers its just a matter of being very carefull to get them in the right place.
When pulling the hood tight for marking be carefull not to pull the screen back and out of alignment. you could use a brace to try to stop this from happening.
Just go slow and measure many times and you will get there.