The most effective evangelists are those who have actually used the tools they're speaking of. And I mean more than for "hello word".

Let me say this: I went to a meetup several months ago for an Angular event. The speaker was horribly unimpressive; quite literally copy and pasted code from the Angular Demo site in-front of us for the "demo", and couldn't answer in-depth questions. No one liked this "evangelist".

In short; have a conviction for what your evangelizing, and dig deep into it.