Basically it's quite simple:
Open your render camera node and keep it open or write down its coordinates.
Import your model of interest and go to the object node.
In the translate field you enter the same values as your camera's coordinates. Now your camera is right in the middle of your model.
Move your camera carefully backwards using the mouse and key controls. The boundary box of the model should show up (check if it's activated "show b-box in preview").
Double click on the cross at the base of your model, you'll now see 3 axes in green, blue and red and the b-box's lines also turns yellow.
Click on the X or Z axis and move it a but further away from the camera.
Now click on "view camera" under your preview window to restore your original p.o.v.
You now also have your model in your preview window and from there on you can finetune its positioning.
It looks like a lot of actions but in facts its really easy and only takes about 10 or 15 seconds.
If you have any troubles, you know where to find me
Martin