When you stand up in front of your co-workers or your class to do a presentation, it helps to speak more slowly than you would in conversation. This makes it easier for your audience to absorb and digest what you’re saying, and it’s especially important if you’re putting a lot of information out there.
The same is true for GMing. Go too quickly, and your players won’t pick up everything you’re saying.
Next time you’re giving out background info, reading a large block of flavor text or otherwise imparting a lot of information in your game, try speaking a bit more slowly and lengthening your pauses between sentences. You might be surprised at the results.