The first thing to consider is who else might be talking on the same forum. Contact them or their speechwriters to get a sense of how they are organizing their talks. You might want to mirror them or take a detour from their approach.
The second thing to consider is what kind of speech the audience likes. If it's a cerebral one such as at a major university they might expect essentially a presentation of the highlights in the field of research on the urban rat. If it's a business one they might an in-depth analysis of the macro economic conditions.
Okay, you have done your "due diligence" about what the context in which you are speaking. Now you can look at some of the ways to organize your own unique talk.
One is the Problem-Solution approach. You describe a problem, making explicit how it relates to the audience. Then you provide the solution as you see it.
Another is a list such as breaking developments in X field that the audience has to be aware of. Then, after 20 or 30 minutes, you open the discussion to the floor. You are hoping they can make sense of things.
A third is a stroll down memory lane. You are invited to recount how corporate life used to be in the 1970s, before downsizing. Here you can enrich the presentation by having members of the audience each present one brief memory before you start your own talk.
A fourth is a hybrid you create. It could be multimedia. There are video clips, tweets you send out during the talk, a slide show, audio of an old Sinatra song, and ongoing live input from members of the audience.
No, you're still not ready to start writing. Run this tentative plan by those who have a feel for public speaking. Ask them if they sense that it will be compelling. What's in our head is in our head. It may not transfer to oral communications.