Drools expert doc has a first chapter that adresses these questions (section 1.2), or at least the questions that must be asked at start of a project.
It covers in details the main key question : rules or not ? Using rules implies more constraints on IT because you allow more freedom in business logic part, so you need a more robust IT code.

Best pratices are then edicted by the architect, this last one having in mind the requirements of :
    - business users (most important as they specify rules, at least some representatives samples),
    - the people who will write the rules (very very important if they are the business users, who are not IT guys, which to me forbid the usage of salience or groups or functions ...)
    - the other IT guys that will provide data streams to your new application, or who will call your app (it can bring constraints because of data volumetry by instance)

In fact, you can't start a real rule project without having enough material in specifications, but this is also true for any project.
So there is no (in my opinion) "global best pratices" (as there is no global best pratices for a random IT project...), with eventually an exception for no-loop (its usage generally shows a lack of design, again, it is my opinion, and I already used them anyway...).
Once again, as Davide said, it depends of the usage. So it seems barely impossible to edit (and keep up to date) such a section with all potential use-cases ...

May be create a rule application that deduce best pratices  ;)  ?

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