Print quality starts with the design of the printed piece. We recommend using Adobe Illustrator or Adobe InDesign. Most issues that effect print quality are a result of the colors used and the the quality of the images.
It is also important to use high quality images. We recommend using images that are at least 600 DPI or the highest resolution images you have available. The use of lower quality images can result in blurry or pixelated images once printed.
It is also very important that the colors used are CMYK. RGB colors that are used in web design will need to be converted to CYMK to be printed and could be slightly different than expected. It is also important to note that your computer output RGB images so comparing a printed version to the version you see on your computer may be slightly different.
To save your file with the correct color settings we recommend converting all colors to CMYK. To do so on the output tab of your export menu select Color Conversion: Convert Colors to Destination (Preserve Numbers). The destination will typically be U.S. Sheetfed Uncoated v2 or U.S. Sheetfed Coasted v2 depending on what material you will be printing on. Also select do not include Destination Profiles. If there are spot colors in you art there will be an Ink Manager button. Select this button then check the box to convert All Spots to Process, which will convert all spot colors to CMYK.
Using these steps to export your files will help increase the quality of you prints and ensure that your colors are setup correctly. This is the simplest, most basic method to create high quality print files, but there are others you may select if you have a better grasp on the exact output you are looking to create.