As a general guide, you should allocate approximately the following times to the different sections.
Introduction: 2 minutes
Methods, Species, Study Sites: 4 minutes
Results: 4 minutes. If anything, feel free to devote more time to your results section. After all, this is what you have done that is new and that the audience will be most interested in.
Discussion and Summary: 2 minutes
It helps to think of the structure of a good talk as two inverted triangles:

Introduction
Start off very broadly. Before you even mention your specific study, give the audience a sense of the big picture. What is the general question or issue? Why is it important, interesting and relevant?
The Specifics of Your study
Now that you have set the general stage, you can get more specific and narrowly focused.
Discussion and Conclusions
Get broader at the end. Tie in your specific study to the larger issues that you established during your introduction.
Use graphs - not tables. Tables are difficult to interpret quickly, and virtually all tables can be presented with a more effective graph.
Summarize your data in well-designed graphs. Ask yourselves "What is the main point we want to make with this graph? What is the best way to make that point?"
Graphs that are suitable for publication (or for your lab reports) are generally not suitable for powerpoint, slides, or posters. The writing is too small to be legible. Minimize the amount of dead space on your graphs.
We often hear about information overload, when in fact we are usually referring to non-information overload! Maximize the data-to-ink ratio in your graphs. Concentrate on presenting the data, rather than chart-junk that makes it difficult for your audience to extract the point you are trying to make.
When you show a graph, make sure that you take time to explain the axes before you plunge right in to discuss what the graph shows.
Summary word slides are excellent ways to orient your audience, and they also make your life easier. At a minimum, you should have the following:
Title slide with the title of your study and the names of all the presenters.
Introduction slide: Brief overview of your
Summary slide. Your results summarized in bullet form. These are the “take home” messages you want your audience to walk away with.
Powerpoint encourages people to present stuff in a very bad way – too much writing, and too many fancy special effects (things zooming around, backgrounds, etc.) that just tend to distract from the message. Simplicity of message is the goal. Special effects do not a good talk make.
Miscellaneous
Modified from materials provided by Erick Greene