The Section Box is a fantastic tool in Revit to create an isolated 3D model of elements in your project. If you are using an orthographic 3D view of you model the section box is fairly easy to control by using the grip arrows to drag in and out. In some perspective views it can be harder to adjust the section box.
Irrespective of you view type, if you need to fine tune the section box in a view you can open up floor plan view of you model and if you right click on the 3D view you would like to adjust there is an option to ‘Show Section Box’. This will show the outline of the Section Box and can be adjusted in the plan.
Remember about the Auto-Section Box Addin, a real time saver!!!