Decide for whom you are speaking. In order to get your speech right, you need to understand who you are speaking to. Who are these people? What do they already know about the topic of your speech? How do they feel about the topic? Where are their pain points? What will make them nod in agreement as you speak, and what will cause them to protest? The easiest way, of course, is to google "Write My Speech Online", then you can definitely have a good speech.
Start at the end. What outcome do you want from your presentation? What will people have to do after you've finished speaking? Vote? Buy shares? Go out for a clean-up day? Donate to a charity? Change their behaviour? So that's where your whole speech should be headed. That's the starting point and that's where we're going.
Structure the speech. When you are sitting in front of a white sheet of paper or a blank monitor and find it hard to get started, change your approach. Don't try to write the whole speech in a single flow at once. It's hard to write and hard to listen to. Divide it up into parts. Start by identifying three key chunks. The rule of three works well in public speaking. Three chunks, each dedicated to a key message. Each thesis, should lead up to the key action that we planned with you in the previous paragraph.
But I recommend that each of these blocks, too, be divided into three parts. That makes 9 parts. Writing 9 small parts and licking them to perfection is much easier than dealing with an amorphous cloud of an entire speech all at once. You have an hour and a half for a lecture? That's 90 minutes, that's three blocks of 30 minutes or 9 segments of 10 minutes. Write 9 key points and cover each one in 10 minutes.
You only have 18 minutes, since you're a TED speaker? Fine. Three blocks of 6 minutes, each divided into chunks of 2 minutes. We write talking points.