We haven't delved too much into pattern matching here on Wide Eyes, Tight Wallets, but there's definitely a science to it. Today I wore this awesome new tie from The Tie Bar, but didn't feel like throwing it on with my normal go-to solid whites or blues. So, this morning was an exercise in pattern matching.
There are two big things to focus on when working with more than one pattern. The first is, make sure it's more than one pattern. In general, don't match dots with dots, or checks with checks, especially if they are literally the same pattern (no matching tie/pocket-square sets, no camouflaging your tie into your shirt).
Second, make sure your two patterns are of a different scale. My combo is a good example. The dots are big and spread out, while the checks are small and thin. If the checks were spaced equally with the dots, and in a bolder line, the patterns would run the risk of blending together. If you do decide to match similar patterns (stripes with stripes, for example), this is doubly important.
Sartorialists often add the rule that your tie should always be bolder than your shirt, but I tend to throw that one to the wind and just have fun mixing things up. Another one you'll hear a lot is to limit your patterns to two. Essentially, if you already have two patterned pieces, keep the rest of your outfit solid and subtle. I only follow this loosely, breaking the rule especially often for a good pair of fun socks (along with a patterned tie and shirt). Even my two 'rules' are made to be broken (see Zachary Quinto expertly rocking three different stripes as featured on GQ.com), but if you're new to the game, this is a good place to start.