A special session on scientific paper writing and publication was held at the 95th AAVSO Spring Meeting  in Rockford, IL (2006). As part of the session, staff member Aaron Price presented a presentation on "Creating Effective Poster Presentations". The presentation is available here in pdf , mov , and ppt  format.
Also, the following is based on an article by Robert F. Garrison, Judith A. Irwin, and John R. Percy Journal of the Royal Astronomical Society of Canada, Vol. 79, No. 6, 1985.
A poster paper is a way of presenting a research or education paper by posting text, images, and graphics on a flat surface (usually 1m x 1m) such as a corkboard. It is an increasingly common way of giving a paper at a scientific meeting. Many, and sometimes all contributed papers are given in this manner. The poster paper has some advantages over the oral paper presentation-especially the five-minute oral presentations currently used by some scientific societies. The audience can view the poster at leisure (as long as adequate time has been allocated for this purpose), and the presenter can discuss it in detail with the audience, without stage fright or rehearsal.
It is our experience that the poster presentations given at most meetings range from excellent to abominable. Those in the latter category do not convey their information effectively-and communication is the goal of any paper. They also do not create a good impression. An established scientist may not need to create a good impression, but a more junior one-especially if job-hunting-cannot afford not to. A good poster presentation does not require much more in the way of time and materials than a bad one, especially with the advent of new technology in computers, printers, and photocopiers. It does require a bit more forethought and concern. The following suggestions may be useful.
Before the Meeting. Find out how much space you will have for your poster. Standard sizes are 1m x 1m and 1m x 2m (clearly it makes a difference). Start to gather and organize the images, diagrams, tables, and text which you need.
Choosing your Material. Avoid the temptation to include too much material in the body of your poster. Two or three pages of text, plus a few images and diagrams, are usually adequate. The captions for the images, diagrams, and tables should be self-contained. Often, they can take the place of some of the text. Ideally, each image or diagram should illustrate a single point, and should be contained on a single sheet. You could include two diagrams together if you were comparing them. Avoid long formulae, equations, derivations, or calculations in the text; they can be posted or made available as an appendix, to be read by those who are particularly interested. The same goes for long tables of data. Often, these are better replaced by graphs. One of the advantages of a poster presentation is that you can have more detailed information on hand for those who want it. It doesn't hurt to include an abstract or summary in the poster itself, even though this may also appear in the meeting abstract book.
Organizing your Material. It helps to lay out and organize your material ahead of time. Find an arrangement which is both clear and aesthetically pleasing. Arrange the text and diagrams in logical order. This can be done, if necessary, with page numbers or with arrows to guide the viewers' eyes.
Constructing the Poster.Legibility is a primary concern! The lettering and diagrams on the poster should be clearly readable from a distance of a metre or more. Letters should be 5 mm in size-preferably more. This can be accomplished by using an appropriate font on your word processor, or using an enlarging photocopier. Your diagrams and captions should also be clear, and easy to read. Avoid small, faint type; use a good laser printer if possible. Make sure that graph symbols are large and clear Some computer-generated graphs are very poorly formatted. Colour can add clarity, as well as getting viewers' attention, as discussed below (though remember that a few viewers will have colour-deficient vision). It helps to mount your diagrams and text on sheets no larger than you can carry easily in your briefcase or suitcase. Some people put their poster on a single, large sheet, and carry it rolled-up. It may be more cumbersome to carry it this way but, since the material is pre-organized, it can be posted quickly. Take an adequate supply of thumb tacks. The meeting may not provide them.
Getting the Viewers' Attention. Although some viewers will find and read your poster no matter how bad it is, others (even some with good intentions) may pass it by. You can help your viewers by having a large, clear title which includes your name and institution (and maybe even a photo of you and your co-authors). You can further attract an audience by using a bit of colour in the text or diagrams, or as a border or background. Mounting your material on sheets of coloured construction paper or Bristol board, for instance, can be very effective. You can even use a bit of whimsy or humour, if you like, if it is in good taste. Consider including an image or two of the objects being discussed in the paper, even if it is not absolutely necessary. People still relate to a visual image.
At the Meeting.Find out when you are required to be with your poster, and when you are to put it up and take it down. Putting up the poster late is a waste of valuable time, and reflects poorly on your image. Failing to take it down on time may result in its unceremonious removal by the meeting organizers. If you cannot be with your poster when required, post a sign stating when you will be there, or when you will be back. Also post your mailing address and/or e-mail address, so that interested viewers can get in touch with you. You may want to distribute preprint versions of your paper, or other material, but remember that you will have to transport them to the meeting, and that viewers may use them for scrap paper. A useful alternative is to post a list which interested viewers can sign if they want to receive preprints by mail or e-mail. This is especially appropriate if your poster paper contains preliminary results, and a preprint is not yet available. It has the additional advantage of providing you with a list of persons who are interested in your work.
After the Meeting. If you have followed our suggestions, your poster will be too good to throw out. Post it on a bulletin board or wall outside your office, and encourage your colleagues to do likewise. This provides an excellent method of keeping abreast of each others' research.