Permanently set some Illustrator Settings
Tell me if this sounds familiar; You spend hours working on an Illustrator file, apply all kinds of filters and effects and drop shadows to your designs, and when you get it back from the printer, much of these effects look different.
Sound familiar? The problem is usually a setting called “Document Raster Effects Settings” in Illustrator. This setting controls what resolution and color space all of your filters, effects, and drop shadows are output. To change the settings you need to go to Effect->Document Raster Effects Settings. Make sure your colorspace is CMYK, and set the resolution to 300dpi.
There is a way of making this the default for every single file you create in Illustrator. In the Illustrator Plug-Ins folder, there is a file called Adobe Illustrator Startup_CMYK.ai. Open this file and change the Document Raster Effects Settings, then save it.
Quit and restart Illustrator. Every new Illustrator file you create will now by default have the correct Document Raster Effects Settings.