I've lost count of the number of seminars, group meetings, and journal clubs where I have had to fight off sleep or frustration due to a bad presentation. And I remember that sense of dread I had before and during some of my earlier talks, my stomach dropping as I saw puzzled looks, eyes glaze over and heads nod. Thanks to a number of great mentors, I've learned a few easy changes to how I approach designing presentations, and now enjoy giving my presentations to any audience.
Three takeaway points. To fight going into too much depth, try to think of the three main takeaway points you would like your audience to take from your talk. It doesn't have to be three, depending on your time/purpose, but the fewer the better.
Think about it from your audiences perspective, and how you would like them to answer 'what was the talk about' in just a few sentences. By focusing on a few broad themes, you can get these points across more easily difficult.
Keep it simple. This sounds obvious, but is some of the hardest part of communicating our work. We are experts in our field, or at least on our way to being experts, and also are used to being precise; this leads to our natural inclination to try to explain everything in extreme detail. You can simplify things to only include just enough detail to support this message. Furthermore, make just one point per slide; if you have one graphic that has several points (e.g. a piece of data which you can draw several conclusions from) give each conclusion on an additional slide.
When trying to communicate, we don't need to be as careful as we are in our writing. There may be experts in your audience who will want you to go into more depth on the details, but you can always keep a few slides in your pocket (e.g. at the end of your presentation) if these come up as questions after your talk.
Create effective visuals. Text is the death of a good presentation, as it results in your audience reading your slides, not listening to your presentation. Complete sentences are absolutely not required; Instead go for key words and concepts, and try to tie them with effective graphics. Also, make sure your graphics/effects are there to help you communicate your message, not to distract from it. Some things may seem obvious, e.g. avoid gimmicky items such as flashing text or comical fonts, overdone backgrounds/templates, bulleted lists, etc. However, somethings are less obvious; one can be tempted to reuse figures, especially ones that someone else generated. However, often there is more detail in these figures then we need, aspect that that figure shows. That being said, it's often easier and more effective to generate your diagrams to be our own to simplify down to the points you want to communicate. It is more work, but it the end, will be worth it.
Preparation. Presenting takes time and practice, and preparation. When preparing your talk, I personally find it best to write down in a few words (not a complete sentence) what the main point for each slide. This means to make sure that I get that point across, but does not force me into a script. Then when I am practicing, I use the cards to focus my talk, but allows me to speak naturally and find what flows the best. Time yourself carefully, and get to know if and how your speed changes when you are in front of audiences. Generally, nerves can make people speak faster or slower (personally, I know I speak faster, having grown up on the east coast). Factor this in, and make sure you are in the time allotted.