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 slides 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.