Always work on your computers in well lit areas with no coffee cups or liquids around.  Liquids can destroy your computer if they get spilled on any parts, so try to keep them (and any small children that might spill them) away from your working area. 

Be sure to wear a static strap to help eliminate static electricity which can ruin the delicate electronics inside your computer.  If you don't have a wrist strap, be sure to touch the metal case of the computer frequently to keep yourself grounded and to avoid building up a charge for very long.

I like to use a desk or kitchen table for my work.  That usually provides enough space to spread out the parts that I am working on.