If you want to mix patterns like a pro, here are some quick tips from HGTV & Better Homes & Gardens:
1) Start with one main pattern & pull your colors from it.
2) Choose 3 or more patterns
Use them in odd numbers. Vary the scale of the patterns (i.e. small to large).
Pattern One: Large Scale, this one will make the biggest impact in the room
Pattern two: Should be pretty different than pattern #1 & 50% of the scale (or less) with some of the same colors
Pattern three: Similar to #1 & #2 with two or three of the same colors in the other patterns
Pattern Four (or more): Something in a small simple pattern or texture.
3) Keep with the same color intensity
4) Make sure pattern is evenly distributed in the room
5) Be careful with whites! If they aren't the same shade, the darker one(s) will appear dirty in comparison.
6) Be a cheater with companion fabrics where available.
7) Choose obviously different patterns, so the it looks intentional.