For example:
Speak Easy is a voluntary program designed to increase diversity in tech conferences through dedicated conference spots, mentoring and events - https://speaking-easy.com/
I always find Toastmasters an excellent resource. They provide workbooks that you can work through, and a tremendous amount of opportunities to speak (and get feedback).
I find speaking at conferences scary and it’s great having that practice time at my Toastmasters club. It means speaking on stage in front of people at conferences becomes less scary and foreign.
I saw that video a week before TestBash Brighton.
It made me realize problems in my talk which I hadn’t noticed before, so that video gets a big from me.
I’m not sure if it counts but I’ve found my coworkers to be a very helpful resource. I try to present my talks to them beforehand to get feedback in a safe and honest environment. As a plus they get to know what I’m talking about
I’ve still not been able to commit three and a half hours to watch James Whittaker . Instead, I found this brilliant version. It’s just under 17 minutes and has tonnes of super useful ideas.
As with many things speaking skills are developed by doing, community group or speaking group. It not only gives practice at speaking to groups, but also gives opportunities to develop group and leader skills: participating in group activities, and helping to achieve something greater as a group.