The content is the 'what'. Can you motivate your research with examples of previous work? What is your contribution or approach? Is the work mature? Have you tested out many corner cases? How sound are your results and analysis? Remember, you are the expert.
The design is used to drive the point home. You need to isolate the key points of your talk, simplify them, and repeat them multiple times. You must know your audience and speak to their level. Start with a meaningful outline of your talk that isn't so generic it could be applied to any other talk. Remember that it's impossible to cover all of the details of a 10 page paper in a 20 minute talk - you just want to sell the idea to encourage listeners to investigate further and read your paper.
Finally, the delivery is how you give the talk. Eye contact, volume, pacing, enunciation - it's all important, and if you need practice, join a group like Toastmasters. Contrary to popular belief, oral presentations are a skill you can learn (you don't need to have an innate talent!).
Some tips for improving your abilities:
- Tape your talk and watching it.
- Practise several times with your research group and get feedback.
- Memorize the first 5 minutes of your talk; it will calm your nerves, and the rest will flow afterwards.
- Leverage your nervous energy and adrenaline.
- Work on your flow: motivate your work, foreshadow, reiterate the main points, summarize.
- It's ok to have brief moments of silence, so try to remove unnecessary fillers ("ummm").
- Come prepared with multiple copies and formats of your slides. Test the projection system ahead of time when possible.
My tip is to leave only 3-5 points on a slide with only 3-4 words each (just the most key parts of a phrase!). Some slides can have just a diagram or photograph when appropriate. All that other text you started with? Just put it in the notes section. You can even publish your slide show as a PDF with the notes if you want people to get all the information. Practice speaking effectively with this style of slides and your audience will thank you.