The US Department of Labor has lots of great ladder safety tips on its website. Here are a couple of tips from the site:

Angle

  • Non-self-supporting ladders, extension ladders or other ladders that must lean against a wall or other support, are to be positioned so the horizontal distance from the top support to the foot of the ladder is about 14 the working length of the ladder.
  • For job-made wooden ladders, that angle should equal about 18 the working length to minimize the strain of the load on ladder joints that may not be as strong as on commercially manufactured ladders.

Rungs

  • Ladder rungs, cleats, or steps must be parallel, level, and uniformly spaced when the ladder is in position for use. Rungs must be spaced between 10″-14″ inches apart.
  • For extension trestle ladders, the spacing must be 8″-18″ inches for the base, and 6″-12″ inches on the extension section.
  • Rungs must be skid-resistant and so shaped so feet cannot slide off

Slipping

  • Keep laddrs free of oil, grease, wet paint, and other slipping hazards.
  • Wood ladders must not be coated with any opaque covering, except identification or warning labels on one  side rail.

Other Requirements

  • Foldout or stepladders must have a metal spreader or locking device to hold the front and back sections in an open position when in use.
  • When two or more ladders are used to reach a work area, they must be offset with a landing or platform between the ladders.
  • The area around the top and bottom of ladder must be kept clear.
  • Ladders must not be tied or fastened together to provide longer sections, unless they are specifically designed for such use.
  • Never use a ladder for any purpose other than the one for which it was designed