Prepare in detail, with your audience in mind: If you've thought about your subject a lot, you may feel that it's so much a part of you that no serious preparation is required - that you can wing it, given some sketchy preparation. This is potentially a big mistake. It's important to distinguish between how clear the subject is in your own mind and how clear you can make it to others. These two are sometimes inversely related: the more into it you are, the less you live in the same world as your audience. As speaker, your job is to present your world to the audience, and that involves putting yourself in their place. So pull yourself back, look at your problem as a whole, and prepare an outline that constitutes a guide from wherever your audience will be at the outset to wherever you want them to be at the end.

Motivate everything. A useful way to do this is to adopt an “hourglass” structure for the talk: broad, then narrow, then broad again: At every point in your talk, make sure that whatever you're saying is well-motivated given what you've said before. This generally means starting your talk with a large, interesting question that requires no motivation itself. The talk can then get more specific by telling us what's already known about the question, and what remains unknown. Whatever is currently unknown (or contested or otherwise not yet settled) will motivate your study, which can then be presented in detail. Then once you've presented the results, be sure to pull back and remind us what their broader significance is - how they fit into the large question you started with. Here is a suggested talk template that may be helpful.

Use examples: Examples can be very helpful in getting your points across. They give the audience something concrete to sink their teeth into. I have seen otherwise excellent talks founder because the ideas were presented too abstractly, without proper grounding in clear examples that the audience could immediately understand.

Practice giving your talk, several times: This is really immensely helpful. If you can rope your friends into listening, do. But I would actually recommend doing it alone before you try it on your friends. You will probably feel self-conscious at first, speaking to an empty room. Ignore it. What this practice buys you is the transformation of your talk from an abstract set of points into an already verbalized story that resides in your mind as a clear, articulated whole. It also gives you the chance to find and fix any verbal hiccups you may have in the talk. For example, in the process of giving a mock-talk, you will notice places in which there might be a better way of saying something -- this is your opportunity to change it. You will also have the opportunity to time yourself, which is always useful.

Nervous is normal: If you're nervous before giving your talk, be reassured: everybody is. Even the most seasoned of speakers is very slightly nervous. This is a natural and arguably quite rational reaction to the prospect of revealing the contents of your mind to a roomful of people who have been trained to be critical. I like to think of this nervousness as something you can take advantage of, something you can ride, so that its power is used to your advantage rather than against you. A slightly nervous edge can add zing to a talk. So accept it, and try to make the most of it. There really is no reason it should get in your way, if you've got a clear outline in your mind and on the page.

Exude self-confidence: This may seem a tall order, as I've just told you that you should expect to be nervous. But try. In particular, try to steer clear of hedges such as "kinda", "sorta", "basically" and the like - these often convey very little other than the fact that the speaker is unsure of themself. So you should not only expect to be nervous, you should also deceive us into thinking you are not.

Learn how to say "I don't know": If somebody asks you a question to which you don't quite know the answer, don't try to fake it. Say you don't know. There is sometimes a temptation to give a half-answer, and this can be worse than a simple declaration of ignorance. Egos don't like open admissions of this sort, but it's ultimately in the best interests of everyone concerned. It will keep you out of territory you don't know (yet), and will be less confusing to your audience than a partial explanation.

Learn how to say "shush": This is easy, and sometimes underutilized. If you feel that questions are leading you off your track, inform your questioners of this fact, and tell them you will return to the issue later on. Stay in control. Remember: this is your story you're telling us, and you need to be sure the narrative flows out smoothly.