A good eulogy does one thing: it tells the room who this person actually was. It is not a list of their jobs, not a sermon, and not a performance. Pick a few true stories, say the honest and specific things people recognized in them, keep it to about five minutes, and practice it out loud. That is the whole method, and the rest of this page is the detail.
If you also need to write the death notice, that is a different job; see how to write an obituary.