First step:
Start giving normal talks. Does not need to be tech talk. Visit your local Toastmaster Club and start working on the Competent Communication handbook. It will be fun, do not worry. You will get instant feedbacks, helping you improving. Being constantly on stage gives you confidence: You can do it! It's easy!
Second step:
Tech talks:
- Know your audience: Who will be there? What knowledge do they have?
- Know your topic: Even if everybody understands your speech, there will be some questions in the Q/A.
- Keep it simple: If you cannot explain it to your 9 years old, you do not understand your topic.