Something else to consider for silk screen effect is understanding how screen printing works, and looking closely at some common effects that occur naturally in the process.
Since screen printing is often done using limited colours (1, 2, or 3-4), I would suggest a reduced but well chosen palette as a starting point for your design.
Registration overlap of the colours is also a characteristic of screen printing. So you have areas where two or more colours slightly overlap at their edges creating a "Multiply Effect". Sometimes this is intentional, and when done correctly can be an effective way of mixing a colour for extra colours.
Sometimes the ink doesn't apply completely which can be caused by a number of factors but can create some textured effects where the white of the paper shows through (think of a subtle grunge effect of white).
Not sure if this helps but the above effects can be achieved with layer blending modes (multiply, etc) or using a grunge texture overlay and again using layer blend modes (screen, opacity etc.)
