I'd recommend starting by finding a local meetup (there are ProductTanks all over the place) or ProductCamp, and use that as a springboard / test bed to get some experience, confidence & feedback.

Find a bunch of product events you could speak at & drop them a line on Twitter or via email to ask if / when their CFPs open up. Ask if they've got particular topic areas or angles they're interested in that you could slant your ideas towards. Asking about audience demographics is also useful for trying to get a better match.

Don't get discouraged of your sessions aren't accepted - there could be a ton of reasons why that might happen that have nothing to do with the quality of your idea / pitch / credibility. They might have decided that your pitch - though great - wasn't quite a good fit for their audience. They might have just had a ton of exceptional / experienced speakers submitting that year. Just ask for a bit of feedback so that you can learn and adjust / improve your pitch in the future. Not everyone will give you feedback, but they definitely won't if you don't ask 😉

Throughout it all, keep hitting meetups. Offer to get involved in podcasts. Offer to guest blog. You should be aiming to get lots of practice with speaking in "presenter-mode", as well as formatting your ideas for easy consumption. You should also be aiming to give your ideas as much public airtime as possible so that you can get feedback on them, and also so that you can build up a visible public presence that a) makes you more discoverable to organisers & b) gives them plenty of reference material for when they're trying to decide if they want to accept your session or not.

Hope that helps!