Make sure to plan an introduction and a conclusion. If possible, take a few moments to think about what you want to say to introduce the topic and have some way of concluding.
Make a few notes for yourself on a card, phone, or iPad. Or, text yourself a few single words to remind yourself of the important ideas.
Consider the simple three part outline of an Introduction, Body, and Conclusion, and fit your ideas into that pattern.
Do not try to remember a detailed outline for your entire speech; just remember the order of important points.
Be sure to stop when you have made your points.
If you do not know what to say next, you can summarize and paraphrase what you have just said, and then will probably be ready to move on to the next topic.
Remember that, in most situations, you will know more about the subject than the audience.
Talk like you mean it. In other words speak with conviction. You are explaining your ideas or knowledge and you are an authority.
Relax!