Which actions in Drupal needs clearing the cache?
Strategy is quite easy - clear it when you changed something in code or database. 

Below some popular cases (based on my experience):


you added new content and need to update cached pages, views or blocks (for example you enables cache for anonymous users)
you changed JS or CSS files and you have enabled aggregation
you installed new modules (in this case need to run update.php)
you did modifications in existing module which require update cache. For instance added menu item or implemented some hooks.
you did changes in theme files