How to become a Doula?

So last night I asked if I should become a Doula and this morning I feel more strongly that this is something I want so I'm ordering a book from a reading list to get me started.

I looked at a few websites and mostly found them to be a little confusing (though I did have a headache beforehand) and lacking in some information. Please recommend a method of becoming a birth doula, whether it's best to find a doula and ask to be mentored or better to attend a workshop and how to locate and sign up for one.