Never Mix and Match Prints
Vintage clothing has made a huge comeback, and as a result you'll see a lot of people mixing prints and patterns. Stripes can be seen with paisleys; argyles can be seen with plaids -- it seems there are no taboos when it comes to mixing and matching prints. Think of it as an intentional unintentional look -- it looks haphazard, in a fashionable sort of way.
If you need proof that mixing patterns can be pulled off, then look no further than Clinton Kelly from "What Not to Wear," who often can be seen with different patterns on his shirt, tie, vest and jacket, all at the same time.