* Avoid making comparisons between your
  children.

* Encourage the children to work out their
  own differences.

* Avoid taking sides on sibling conflicts.
  Be impartial, and do not show a
  preference for one child or another.

* Set guidelines on how children can
  disagree and resolve conflicts.

* Discourage tattling.

* When it is necessary to punish or
  reprimand, do it with the child alone in
  a quiet, private place.

* Use regular family meetings for all
  family members to express their thoughts
  and feelings, as well as to plan the week's
  events and to give positive recognition and
  rewards (allowance, special privileges).
 

(Source:  American Academy of Pediatrics Caring For Your School-Age Child, 1995)