Mixing patterns is NOT easy. But, it makes for very interesting decor palette in any room. Here are some rooms that have done the "mixing pattern thing" very well. They all have a sense of cohesion that is hard to get if unless you really know what you are doing.
1. I am in awe of this bathroom. I am sure this is a wallpaper, but I can't imagine why someone would spend the money on this particular wallpaper when this pattern would be so easy to do yourself with a stencil and some paint. The gold spots really pull out the golden tones in the shower curtain and it is not too much pattern because they stopped after the wallpaper and the shower curtain and did a plain white rug.
2. Love love L.O.V.E. wallpapered shelves. It is so easy and it can even be more affordable if you can use scraps or get smaller leftover pieces (I guess those would also be considered scraps). You could also paint or stencil onto the back of a bookshelf (which would be A LOT more affordable). This space works because they stuck with a few different colors and then chose different patterns to mix. The blue in the bookshelf pieces, the throws, and the rug ties in with the brown very nicely.
3. This space is very simple but elegant. The pillows are mostly black and white but with a touch of teal (also in the rug in a slightly different hue). The walls are really stark and there is a lot of white in the room, so the pops of color serve to really brighten up the space and give it some flair. (Love the mirror on the center wall, too!!!)
4. This picture only captures snapshots of a few mixed patterns throughout these two spaced, but you can see enough to know that it all works. Tufted headboards are so pretty and the hot pink is such a statement. The plain wall behind the headboard leaves room for some pattern on the throw pillows (oranges, grays, and lime green) and the black and white zebra rug. The bathroom wallpaper plays off the colors in the bedroom rug, with another pop of the lime green in the small stool under the towel rack.
5. Mixing throw pillows is an art unless you are either carrying them all around with you all the time until you find the perfect mate, or you buy them all at the same place on the same day. Unlikely. The last time I was buying pillows I went to Walmart and picked up a bunch of free color samples that I thought would match the pillows I had (I took a picture on my phone to go off of). When I got home, I picked the one that was closest to the colors in my throw pillow and kept that in my purse. Much smaller than the actual pillows. Plus, if it looks bad when you actually get it home, you can always return them. The mix of pink, teal, gray, and black here is so bold and daring. The pillows all flow well, even though none of them contain the same pattern.