I attended the workshop today titled "Creating Professional-looking Conference Posters" taught by Rob Pettigrew of the Digital Media Commons at the University of Michigan. I learned the basics of Adobe Illustrator, specifically for the task of creating a conference poster. Rather than write up yet another intro to Illustrator, of which you could find dozens online, I'll convey four technical tips that should be taken into consideration.
1. Stick with vector image formats
Vector images (.eps, .svg), as opposed to bitmap (.jpg, .gif, .png, .tif), can be stretched to large sizes without giving up any quality. Bitmap images are the type that you download from Google Image search. A more detailed discussion of the differences between vector and bitmap can be read here.
2. Create graphs in dedicated graphing applications
Following the discussion of vector vs. bitmap, you definately want to create your graphs in vector format. That means don't create a graph in Excel and then copy and paste it into your poster! Excel has problems with copying and pasting into Adobe Illustrator, as I learned today. If it works at all, it exports bitmapped images that can't be stretched without looking pixealted. Instead, use SPSS or other graphing software that your department owns.
3. Know RGB vs. CMYK
Without getting too geeky, RGB is the color space used in computer displays and projectors, while CMYK is the color space used in printing. Converting from one color space to the other can lead to colors you didn't expect. For example, if you tried inserting a color gradient in your poster, don't be surprised if the printed version has color bands.
Stick with CMYK in your poster and keep your colors relatively simple. No gradients!
4. Use the right software
Today I used Adobe Illustrator. I'm sure other software packages would do a fine job as well. PosterGenius seems highly regarded in the scientific community. Old heavyweights like Quark and Adobe InDesign are also good choices. Probably the best advice is to seek help from whatever instructional technology support infrastructure exists at your institution.