Student research talks may be one of the few times where you can really showcase yourself to the scientific community. Some faculty may know your grades, your PI and lab mates may know about your work ethic, but when you're giving a talk, this is your opportunity to demonstrate to everyone else about your ability to think through scientific ideas and explain them. Therefore, I think it's important to give a good presentation. If you can do this successfully, then you will be seen in a favorable light by the community -- and that will always be a good thing.
-Teach your audience. When you're working in lab, sometimes it feels like there is so much that you don't know. However, when giving your talk it's fairly safe to assume that your audience knows less than you think they do. Therefore, I'd encourage you to think of part of your presentation as teaching.
-Less is more. In the end, simplicity is key. My approach to getting here may be unique. I start out by making many slides and then cutting down. Doing it this way is labor intensive compared to starting small then building up, but I liked seeing everything, then figuring out what's important later. You will eventually figure out which items are best left in and which ones you could do without. If you're having trouble with this, then a good practice audience will let you know. Another benefit to having extra slides is that you can put it at the end of your presentation in case people have specific questions on things that you don't have time to cover in more depth.
-Transitions, transitions, transitions. Good transitions in a presentation serve the same purpose in an essay: they signal a change in topic and help ensure that your audience's attention is not lost during this process. If transitions are not done on your slide, then state them verbally.
-Take advantage of Powerpoint features -- but don't overdo it. Properly used animations can help maintain audience attention. Entrances facilitate in drawing attention to figures and text while exits preclude them from being a distraction. They can also be used to help explain data. For example, you may want to explain how the levels of a particular protein are affected by different treatments. People usually explain the effects of each treatment one-by-one; you also have the option of doing this visually with Powerpoint features. But do not use so many animations that they become a distraction. And stick with simple animations. Anything too flashy can be disconcerting to an audience.
-Ensure that your presentation is compatible on the computer used to present. Often, one may make a presentation on one computer but then borrow a friend's laptop to do their presentation. For example, if you create a presentation on a PC but then transfer it to a Mac, animations or symbols (such as Greek letters and arrows) could be lost. Do not wait until the last minute to run your presentation through the computer that you will use so that you can edit if necessary.
-You can never practice too much. The more practice you have, the more comfortable you will feel, and the better you will deliver your talk. It's important to practice in front of lab members. However, I find that practicing in front of scientists that do not know your work provide very good advice since they will be very similar as an audience to your actual presentation. An audience with a diverse scientific background will also give you different kinds of feedback.
-Use the question-and-answer period to help you. Nervousness is normal when handling questions. But you may be surprised to learn how beneficial this period can be. Although some people may ask you questions as a way to provide constructive criticism, I've realized that usually people are just curious and interested in what you're doing. Questions will also help you see things in a different light or help you consider using a different technique. Therefore, I embraced this period during my talk and I actually requested that some faculty attend so I can get their feedback. Even if you capture this mindset, you may still want to do things that make you a bit more prepared. Knowing your project very well is the best preparation: talk to your PI and other lab members about your data. This ensures that you know the nitty-gritty of your project. Also, a practice audience (as discussed above) will often ask the questions that your SRT audience will ask. In fact, I had a couple of questions in my SRT that others asked during my practice talk. When this happens, you can be prepared to handle it like a pro! But no matter how much you prepare, you may still encounter a difficult question. Do not worry. If you handle it with tact and grace, you will be fine. For example, if you know literature well you could provide your opinion on the issue so long as you say that it's your opinion. But a simple statement such as "I'm sorry but I don't know the answer to that question" will also work.
Seize opportunities to give talks, whether it's in a lab setting or in other situations. As with anything, confidence comes with practice.
If you see someone who's a good speaker, don't be afraid to ask them for tips. Many good speakers would be willing to help others improve their presentations.