How to use Tempo site effectively?

I'm not sure what you mean.  The /Tempo "my tasks" list will show only tasks for which a person is an assignee, either individually or by list/group.  Process Security would override this in every case that I know of.

Current best practices are, really, "don't use tempo".  If you DO want to use tempo, you will probably need to structure your entire setup around this.  My first project was an entirely Tempo based system, so I know it's possible.

My experience in recent years tells me to just not use Tempo. While I like the idea of enterprise wide collaboration, I just never got my clients to accept the required change in working culture.

Now we create one or more sites per application and once we have more users who use multiple applications, we somehow recreate tempo as users want a landing page on which they can find all their tasks in one list. Then we discuss how to get rid of all the task report customizations we had to implement before.