Is there anything I can do to keep my 4 color Process prints from looking dark and muddy?

Most problems in Process printing are a result of incorrect separations. Computer Graphic programs will default to SWOP color; an ink set use in offset paper printing. So generally, separations are created with one set of inks and printed with a set of inks with different hues and strengths. Loading Process color values is a major step in creating accurate process separations. 

Adobe Photoshop allows an artist to load Process color values, which are the color positions of the ink that will be used in production. Most ink manufacturers offer color values for their Process inks, which can be downloaded from their web sites or sent from their Technical Services department. These values are free. The color values will differ with mesh counts, so you must know which process ink set and what mesh count your production department intend to use. There are two other tricks will help with a Process job on press. One is adjusting the black plate. Black was never meant to be an equal partner in CMYK. It is very important to allow CMY to take care of the subtle grays. Using Curves, adjust the black channel curve to start at the 25% mark; this knocks the black out of the lower 25 percent of the gray areas. Another trick is using a Wet White. This white is a first down white, followed by YMC then K. A wet white plate will include all white and pastel colors in the design. When the inks are printed, the wet white will mix with the process colors to create nice color tints and will keep the dot gain in those areas to a minimum.

The bottom line on most application questions is "Ask the source." Nobody can help you quicker than the people who manufacture the product. Keeping product information on file for quick reference will spare many hardships also, so require your distributors to send you a Product Information Bulletin with any product you receive. Common sense must prevail, but never think that you are better off being safe rather than sorry by manipulating an ink. In some cases you can be introducing another group of potential problems.