Plan your presentation
The starting point of too many presentations is to copy and paste slides from already badly planned presentations. Before sitting in front of you computer, have a think about what you want your audience will want to gain from listening to your presentation.
Try putting all your ideas on to post it notes stuck to a wall. This way you can easily move your ideas around, getting them into the right order.
Directing audience using animation, at the same time not over animating your slides.
There are two types of animation, moving or static. 'Fade' is a nice animation to use (a static animation) when revealing new information. It's very rare that a 'whip' or a 'Spiral In' is going to add to the content of your presentation!
Clip Art (Curious little irritating pictures annoying random tacky)
Clip art has become a lot better over the last few years. PowerPoint now even offers 3d models to add to your presentation. However, make sure you take some time to get relevant pictures which support your message.
It is no longer acceptable to add a badly drawn picture of people dancing to the corner of a slide, just to try and make it a little more interesting & colourful!
There should be very little text on your slides anyway. Where there is text, unless it's a quote, try and not read it out verbatim. It's boring & disengaging if you read from a slide too much. And worse, it could show a lack of knowledge and confidence.
Hopefully you will know your presentation well enough to talk from your heart rather than a slide.
No sentences & no punctuation. If you do insist on using bullet points, they definitely DO NOT need a little dot at the start of each one. If you bullet points have punctuation in them, they are TOO LONG!
Also check your font size, point 8 may look ok on your computer screen, but probably won't on a projection screen. Keep your font size above 20 if you can.
Keep for text direction, as you would read it, no need for head turning. Also avoid capitals. Capitals are a shout in any language.
Have a slide that can sum up your message quickly. You may not always use it but have it as a reserve in case the CEO walks in half way through your presentations wanting a summary then to leave.
Once you've used your killer slide you can skip back to where you left the presentation.
Presentation length does depend a lot on what you are doing and trying to achieve.
If its a sales pitch limit it to 25 minutes. If you are delivering. If you are delivering a days training have a hard break (get out of the room away from training break) around every 45 minutes, and incorporate soft breaks (videos or working in a group) in between.
Remember, your time and the time of your audience is precious. Use your time wisely and don't waste time on saying when your company was founded or it's annual turnover.