There are many different tips and tricks for improving performance in AutoCAD Civil 3D. This tutorial will cover two of the most important ones that you can implement quickly and easily.
Set PROXYGRAPHICS to 0. PROXYGRAPHICS is a drawing variable that specifies whether to save proxy graphic images of objects that can not be displayed by basic AutoCAD. In Civil 3D this means that if PROXYGRAPHICS is on (set to 1) then you are saving images of surfaces, points, alignments, and all other Civil 3D objects. This results in much larger drawings and decreases in performance.
If you do need to share drawings with AutoCAD users, consider having them install the Object Enabler so they can view the objects natively or using the Export to AutoCAD option, which explodes AutoCAD Civil 3D objects to AutoCAD primitives.
PROXYGRAPHICS is a drawing based variable so it needs to be set in each drawing. You should also set it in your drawing template so that new drawings are created with the variable set properly.
Set LAYOUTREGENCTL to 0 or 1, but not 2. LAYOUTREGENCTL is a system variable that controls the caching of the Layouts in your drawing.
If set to 0, the drawing is regenerated each time you switch layouts.
If set to 1, the Model tab and the last Layout made current are cached.
If set to 2, all Layouts and the Model tab are cached.
Caching the Layouts does prevent a regen when you switch between tabs. However, it also uses up precious system resources that Civil 3D can use to improve performance and stability.
LAYOUTREGENCTL is a system variable so you only need to set it once on each computer in your office.