I'm happy to share this useful set of patterns for all - it's based on the default dot set that comes with Illustrator. The difference being that the dots are all set up in Cyan, Magenta, Yellow, Black, and White so you can easily overlay them onto each other (hint - 100% multiply looks like printing). And if you transform patterns (Effects>Distort & Transform>Transform) you can easily change the screen angle and size (make sure Transform Patterns is checked!).
Get it here http://d.pr/f/9ZEb and enjoy!
Oh yeah, put it in Adobe Illustrator/Presets/en_US/Swatches/Patterns/Basic Graphics to find it real easy. Then go to your swatches panel and open swatch library and navigate to Basic Graphics_Dots_CMYKW.ai
This has helped me a lot with designs - hope it helps you as well!
Also, if you like this, please follow me...