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Choosing different prints in the same color family gives the look cohesion. (Especially if you pick a brighter color like this lemon icing-y yellow, you'll want to keep accessories simple and your handbag neutral. Your outfit's already eye-catching enough.)
If matchy-matchy's not your thing, choose a striped accessory that picks up a shade from a multicolored floral dress (or vice versa). It'll communicate that you paired the prints intentionally, without looking too full-on stylized.
For a look that's less "Olivia Palermo at an Oscar de la Renta show" and more "Kate Bosworth at Coachella," choose florals that are more laid-back than punchy, and pair them with equally "I'm with the band" accessories.
To spin the look a little more sophisticated, stick to a classic black-and-white palette. (Choosing things like slim pants and polished heels helps, too.)
Of course, you could always just go ahead and buy a dress/top/skirt that knocks out the print-mixing for you, all in one piece. (But then what would you mix it with?)