Inspired by a thread at gmaxsupport.com, here are some handy mouse and keyboard shortcuts to save you time...

• Press W to maximise the current viewport. Hit W again to return to the normal multi-viewport view. Great for detailed work!
  
  
• Hold down the middle mouse button to pan around
  
  
• Hold down the ALT + middle mouse button to rotate. You can change the type of rotation (eg. to around selected object or subobject) by using the rotation flyout at the bottom of the gmax screen.
  
  
• Scroll the mouse wheel up and down to zoom in and out
  
  
• Hold down CTRL + ALT + middle mouse button to zoom in and out smoothly. This gives much finer adjustment of zoom than using the mouse wheel.
  
  
• Press G to toggle the grid on and off
  
  
• When in a viewport (eg. zoomed in after pressing W), you can quickly change its type by pressing the following keys:
  
  
  • P- Perspective view
  • U- User view
  • F- Front view
  • K- Back view
  • T- Top view
  • B- Bottom view
  • L- Left view
  • R- Right view
  
  
  
• Hit X to toggle the "gizmos" that appear at the origin of selected objects. Gizmos are used to restrict which axis is used for rotation, translation or whatever tool is active.
  
  
• When in Edit Mesh mode, you can quickly switch between editing levels by using these keys:
  
  
  • 1 - Vertex
  • 2 - Edge
  • 3 - Face
  • 4 - Polygon
  • 5 - Element
  
  
  
• Hit ALT + B to quickly bring up the Viewport Background Dialog. You can use this to set up reference images for each viewport, change the viewport colour and ambient light settings.
  
  
• I've never seen this documented anywhere, but if you hold down CTRL + roll the mouse wheel in a MAXScript window you can zoom the font size in and out! Not entirely sure how useful this is, but it's quicker than using the preferences dialog!
  
  
• Hit M to bring up the materials editor