So much of what I and many other Computer Scientists do is give presentations. When I worked full time, I prepared at least one presentation a month, often more, and wrote regular reports of my work for upper management. As a grad student, I give fewer, but still write many papers.
Not to say I'm anywhere near perfect at presenting, but I have come a long way in learning how to write and present, skills that I once thought had no relation to my profession. So let me again refer to another blog that outlines the time and steps required to prepare these presentations. Many people think they are ready to present with a just set of slides and skimp on these steps. I've sat through "dry runs" where the presenter hadn't even practiced. Or even presentations where the presenter isn't ready. So take the time and practice, otherwise we walk back to our desk and laugh about the latest speaker that we didn't understand.
