How to make power point presentation most effective

Have one source of information
Your audience should know exactly where they can expect all the information to be coming from. It is either the slide, or the speaker, or the surroundings, or the product, or the concept. Make it clear where all the new information will be coming to them from, and try not to have multiple sources.
Make yourself the center of attention
With the above, it is always best to make yourself that primary source of information. Your words, and how you are presenting them, must be the only place where people get the message from
Use PPT only to support or aid you
If you are the sole source of information, then you dont have to put any text on the slide. Use the slide as the place where yoru audience finds supporting information to what you are essentially saying. Slides that only have a picture or chart are great.
Pace the PPT slides to tell everyone the basic topic you are discussing
If you are the center of attention you could go through the entire presentation without switching a slide. However, that is a good way of losing the audience. Since your message will be delivered in parts, or categories, or sections, make sure you put a four-to-five word title sentence on the PPT that defines that section / topic / particular point.
Use timing queues liberally
Quite often a presenter dives into a slide with a mesh of information, and then starts to explain each portion of it one at a time. What he doesn’t know is that the audience stop caring the second they see complexity. Use the animation and timing functions in PPT to show them only small easy-to-digest portions of the slide at any time.
Keep note of image aspect-ratios
This is particularly true of internal ppts. If you are adding images, make sure they are not bent or distorted just to fit on screen. If the audience sees a distorted image, they will start spending too much time understanding the picture rather than understanding the message.
Make everything have a single theme
Is the presentation going to be light to begin with, or is the presentation topic “Characterization models of third-stage cancer using noise-impeding feedback in fuzzy control systems” ? If you begin on a light note, then you, the slides, the timing queues, the animations, should all be light. If it is a serious or corporate theme presentation, then everything should be complementary — resist that urge to ‘add that random funny picture to relax the audience’. Coherency makes the audience feels relaxed about you.
Understand the importance of the delivery tone
How you speak is more than often much more important than what you speak of. Your presentation is essentially guiding the audience through a series of concepts in a way that they can come to the same conclusion that you have. This ‘guiding’ is most relevant with the way you deliver context.

Use a Whiteboard liberally
They great thing about using whiteboards is that your draw-as-you-speak — so the supporting pictures your audience sees is in perfect timing with your own words. You can do some of that in PPT with animations but it is not enough.

Most importantly, keep yourself in constant check. Always try to measure the ‘impact’ of the presentation from the reaction of your audience, and keep improving the presentations over time.
There are lots more, but this would be a general set of guidelines to get you started.