The goal of an academic talk is to communicate your ideas, and to convince others that your approach has merit.
Doing the following will generally help you give a more effective talk.
General talk advice
You should know the material of your talk well before you give a talk. You should know the order of the slides in your talk, and you know how you will transition from one slide or point to the next.
Practice with an audience
It can be difficult to critique your own work. Give practice talks to them, and encourage them to give helpful feedback.
Presentation software advice
Most modern talks are given with the support of presentation software, such as Powerpoint or Keynote. Your talk will be judged as much by what you say as by what you show, so creating a well-designed presentation is of great importance. Standard rules of good writing generally apply to the text you put on your slides.
Make your slide text legible
When you create your slides, you are most likely only a few feet from the computer screen. When you present, the audience will not have as ideal viewing conditions, and as such, you should avoid having small fonts.
Make your slides visually appealing
While you are not expected to be an expert artist, following basic graphic design principles will make your slides more pleasant to look at, and will influence how others see your work. Spend the extra time needed to make sure you and others like the way your slides look.
Put key points on slides
Your main point on every slide should be written on that slide. Some people may only read the slides and ignore what you say. Having something written on the slides will emphasize that it is a key point and that you want others to remember it.
Pause when switching slides
When you switch slides, many members of the audience will immediately ignore you and read all the text on the screen. If you pause for a few seconds when switching slides, you'll be giving hopefully enough time for people to quickly scan the slide and then pay attention to you. However, this is not always the right approach, especially if you have a good logical flow between slides and are able to maintain the audience's interest.