I believe firmly in the philosophy that one is an eternal student, always learning, and one should therefore always be open to improvement. This is particularly true of presenting your data to the scientific community. After all, your data may be awesome, but if it's presented shittily, it will be less well received, or maybe even looked over. Some of my student colleagues may disagree - they think that their presentations are "good enough" and the data will stand for itself. Bollux! I, for one, am not going to stand at a poster for 20 minutes trying to puzzle out which band is which and wonder what the hypothesis even is, if the poster is not clear. Furthermore, a good presentation will jump out and grab viewers by the gonads, exciting them in your work and further engaging them in your science. A poster that is boring or hard to follow won't get stopped at as much, and a presentation that is bland or overly complex won't elicit the types of engaging questions the presenter might want - after all, who wants to spend their 5 alloted minutes for questioning rehashing their presentation?
I also wonder how many scientists have any sort of formal training in oral or poster presentations. I am willing to bet the large majority does not, and instead relies on apprenticeship to gain presenting skills. This is great if your mentors are good presenters, but this is terrible if your mentors are horseshit presenters. I'd argue that even if your mentors were good presenters, there are still improvements that can be made. First, your mentor's style, while it can inform yours, can't be your style; you need to find your own voice, early and often. Second, I have noticed many faculty present in the style that was popular when they were in school or doing their postdocs, leading to an overwhelming amount of comic sans, complexly arrowed diagrams, too much text, and design that is incredibly red-green colorblindess unfriendly. Hell, I first learned to do my presentations in the late 90's-early 00's and am guilty of many of these mistakes. Relying on outdated methods/styles should be avoided at all costs, as it reflects complacency and a lack of refinement of personal skills.
In my quest for presentation skill knowledge, I recently came across two incredibly helpful blogs: Better Posters and PowerPoint Ninja, both of which have gads of presentation style pointers as well as technical advice. Aside from my #1 rule of thumb - never say in text what you can say with graphics* - there isn't really much more advice I can add to the subject than has been covered there, so my advice is to get your ass over to those blogs and play around for a few hours. They're pure awesomeness.
Discovered via Ambivalent Academic.
*Let's be real: NO ONE reads the text after the section/slide title. You can test this by inserting jokes into your poster figure legends (or, as a student colleague did, into the footnotes of your thesis - only her student reviewers noticed).