To solve a really ugly bug of the video module I had to track down, in a very detailed way, what was the hook execution order in the Drupal 5.x hook_nodeapi. Unfortunately I didn't found any detailed documentation of this neither on the handbooks nor in the developer documentation (on CVS).

This is why, armed with a lot of patience, I wrote down what happens at every content submission/previewing/loading.

Those are my results:

node submit (validation successfull):
prepare form validate submit insert

node submit (validation unsuccessfull):
prepare form validate

node/add/type (first visualization):
prepare form

node preview new node (validation unsuccessfull & successfull):
prepare form validate

node view:
load view

node edit:
load prepare form

node preview existing node:
load prepare form validate view

node submit existing node:
load prepare form validate submit update

UPDATE 1: Posted a feature request to the documentation team to insert this informations somewhere in Drupal documentation.

UPDATE 2: Please note that the form operation above is not available on the hook_nodeapi. It's just mean that the form is being constructed at that time. If you need to interact with the form (eg: adding/modifying form fields) you can do it using the hook_form_alter