The availability of free and open source art packages for PCs and Macs means that anyone can design a good poster and illustration today, however, printing a poster can be tricky. If you’ve ever tried to print a full color image, like from http://www.illustratedmapart.com, on a desktop then you have probably experienced some of the problems. Images that look good on a computer screen don’t always look good on paper, and while you can get away with printing a low-resolution file on A4 paper, you may get jagged edges and other quality issues when printing a full sized poster.
Here are a few tips to help you print a good poster:

hoosing the Right Poster Size

The best size for posters, usually, is A0. There’s no need to print a poster in 8’ x 4’ format unless you plan to use it at a major trade event or in a concert all. Printing your poster in A0 size ensures that it’s easy for people to see the poster because the main content should end up being at eye-level for an average sized person.

Fonts and Lettering

The minimum text size that you should use on a poster is 24 points. Anything smaller will be un-readable. The main heading on the poster should be at least 72 point size.

Preventing Quality Loss When Printing

Posters, especially ones with a lot of color in them, should be printed on thick, glossy paper. When designing your poster, use a minimum of 300-400dpi (higher is better). If you are designing your poster in a fairly small format such as A3, bear in mind that it will be enlarged by 280% to create an A0 image. This will result in quality loss. If you must create an image in a smaller format, use the highest DPI you can, and choose an aspect ratio that is identical to your intended final size.
If possible, use vector graphics rather than bitmap images, so that you can re-size the images easily. In addition, save in a loss less format. Do not use .jpg to save images that are intended for print.