Everything I know about mixing and matching in fashion comes from the long dead Jane Magazine. Way cooler than the teen magazines and never at pointlessly skanky as Glamour (sexy with purpose - that was Jane). I scanned in a bunch of my magazine tears a few months ago and couldn't bear to part with these. Circa 2006 and 2007 and still looking fresh.
For me, it was barely even about specific pieces (though I desperately wanted that little peach slipdress when that issue came out). It was about the versatility in layering, especially by mixing things that DON'T MATCH. Pretty little dress + tough jacket. Work pants + boho shirt.
And I think that's how I decorate too. Pretty floral + mid century modern. Jute rug + glass table. Traditional chair + stump as side table. Life is just more interesting with a little juxtaposition.