I have done pit firing at school. Other than the obvious safety measures,
monitoring the fire, etc, the main pointer I would pass along is to be sure that
sufficient oxygen is available in the pit. I once had a really good pit firing
with a relative shallow pit, although, even then it was difficult to get the
fire going well to begin with. (It is helpful to soak some sawdust in lighter
fluid ahead of time and use this to start the fire, but of course use proper
precautions as this is a very flammable substance.) I also had a not-so-great
firing once in a pit that I realized later was too deep (less oxygen).
One possible solution to getting enough air into the pit that I have seen,
but not tried so far, is to use a fairly large-diameter metal pipe or pipes
which extend out of the pit a short distance and thereby allow some oxygen under
the layers of sawdust and pots. As I said, I haven't actually done one this
way, but from my pit-firing experiences it seems that the pipes might help.
Jeff in Georgia