You may have great content, smooth delivery, great audience connection, a sharp outfit, well-groomed eyebrows and a well-rounded sense of humor, but if you're going to write on a flip chart, white board or overhead, your handwriting better damn well be legible.
I heard about a seminar recently where the speaker was all of the above. Then he started writing on a flip chart and his content went out the window. Interestingly, during that workshop, a video was shown of the speaker giving an earlier presentation, and his writing was equally illegible. So it wasn't just a one-time, guy-in-a-hurry type thing. His handwriting was always bad, and he just didn't care.
If you're going to use a flip chart (and flip charts are great for recording audience interaction and saving notes to refer back to during the presentation), then print large, clear letters, and write slowly. If you know you have sloppy handwriting, make a conscious effort to write more neatly. If you think your handwriting is neat and tidy, STILL make an effort to write more neatly.
If it's easier for you to write neatly when you write small, consider using overheads or a tool like Papershow, that allows you to write on paper but show it on the same screen where you're showing your PowerPoint.
It's a tiny detail, but it makes all the difference in whether the audience is able to follow your ideas.
Here's a nice short video with a great tip for making your writing more legible. And below, a video with additional flip chart tips. Enjoy!