These will come in handy. 

• If you can shoot through a wall, then shoot through it.  Don't keep waiting for people to peak.
  
• Use a headset.
  
• Learn footsteps - I'd recommend downloading transparent textures, creating a server with bots, and watch them through walls to study their position relative to the sound of their footsteps.
  
• I rarely record wallers, but when I do I use transparent textures while reviewing the demo.  See http://www.youtube.com/watch?v=8OQKhA6vL0M for an example of what I mean.  A member of the 47r team with a little walls - they still deny it.
  
• Bunny Hopping?  Bind jump to mouse-wheel down.

There are a LOT more - most of the tricks you'll find in CS will come through experience.