Designing for Wide Format output is not difficult - it is just a much bigger page size. There are a few things you can do to ensure that the quality of the output matches the intended use.
Getting the resolution correct is where most people come unstuck. For best results we suggest that images are supplied at a minimum of 100dpi and a maximum of 200dpi at the final size.
"At the final size" is the key point. If you are designing your poster at it's final size (eg you are wanting an A1 size print and the dimensions in Photoshop are 594mm x 841mm) then your resolution should be between 100ppi and 200ppi
However, if you are designing at a smaller size and intend that your image is to be enlarged, then you need to multiply the ppi by the scaling factor. For example, you have an A4 image in Photoshop that you want to be printed at A1 size: this will require a 283% enlargement (841mm/297mm*100 = 283%) so the resolution will need to be between 283ppi and 566ppi (100ppi*283%=283ppi 200ppi*283%=566ppi)
Please note that if your image resolution is low, your output will be pixelated (blocky looking). The only way to increase the resolution of an image is through interpolation which guesses what the intermediate pixel should be and will generally result in a soft looking print. Keep this in mind when scanning originals - you need to scan at a suitable resolution for output.
If you are putting text over an image within a design application like Freehand, Illustrator, InDesign etc then you don't really have to worry too much about text as these applications use vector text, which allows it to be scaled up to match the output resolution of the printer. However if you are putting text on your image within Photoshop, then you may want to consider increasing the resolution of your image in order to produce smooth text. The amount that you need to increase the resolution to really depends on the point size of the text. We would normally suggest that if you have text in your images then their resolution should be 300ppi at the output size.
We can print either CMYK or RGB files as well as simulate Pantone colours. Our EFI Colorproof RIP is set to assume that your CMYK files are set to SWOP and RGB files are set to AdobeRGB. Please advise if you are using a colour managed workflow and your files have embedded ICC profiles and we can configure our workflow appropriately.