If you have never spoken at an event before, consider joining meetup.com and find relevant meetups. First attend 1-2 meetups to understand their goals, theme, and topics that interest the participants - and then you can propose speaking there.

If you use slides, update your Slideshare profile and it builds your speaking portfolio. Next time, use this Slideshare profile to send proposals to other events - city level, and then regional and others.

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Identify people who are speaking at the events where you want to speak. Engage with them (social, emails, or in person if they are in same city), and exchange value. They should be happy to propose your name as a speaker in future events.

Important: "Value" is the keyword. Good luck for your book!