Step 1: Start in time.
Once you submitted the abstract to the conference organizers, it is time to start thinking about how you organize the material in a talk if your abstract will have been accepted. Read about the background of your work, read related work, look at your own results regularly and think about the most relevant conclusions. Try to imagine what type of audience you would have and consider what you would have to include as background information.
Step 2: The message
Try to capture the message of your presentation in a single sentence. This is difficult. You will only be able to do this if you really master your subject (which is actually the main requirement for being able to clearly present your work to others).
Step 3: Select your material and order it.
Use the ‘message in a sentence” under 2) as the criterion to select which results to include, in what order, what basic information is needed to appreciate these results, and which experimental details are necessary and which not. Be very critical, any experiment or result that does not contribute to your main message should be left out.
Although it may at first sight seem natural to present your results in the chronological order in which you obtained them, this does not have to be the most ideal order for the audience to understand what you have done. Think about where to discuss highlights, at the beginning? Near the end? Maybe dispersing the remarkable features through the entire talk? It is up to you, but take the order which you feel appeals most to the audience.
The scientific background of your audience determines how much you should explain about experimental approaches, characterization techniques. Be careful NOT to identify your audience with your supervisor, the majority of listeners is unlikely to possess much specific knowledge about your subject. By the way, hardly anyone minds to hear something he already knows, as long as you explain it well, and possibly in an entertaining way.
Step 4: Opening and Introduction
In the opening, i.e. the first few sentences, you catch the attention, for example by a scientific question, or a catchy or maybe even provocative statement. Perhaps you could already give the conclusion of your work too. Try to speak slowly, with emphasis, and look at the audience. Of course, you must have prepared and rehearsed the opening carefully.
However, before you give your opening sentence, it is good to start with “Mister Chairman, Ladies and Gentlemen…” followed by a few seconds of silence, in which you look around to see if people are paying attention. By doing so, you actually force the audience to listen. With these words you also test the sound system, and you ascertain that your important opening lines are going to be heard. In the rest of the Introduction, you sketch the background of your research. Remember that many people will be very interested in a concise summary of the status in your area. Hence, reserve sufficient time (i.e. at least 30% of the total time) for the general aspects of your work. It is good practice to not only clearly identify the scientific question you address, but also give the conclusion of your work, if you wish so. In this way you enable the audience to better follow your reasoning and to anticipate on the outcome of the experiments. In other words, you give them a chance to listen actively. Remember that a scientific presentation is not a detective story which is solved at the conclusion.