Das wurde dieser Tage diskutiert, blättere mal etwas zurück. Vielleicht erinnert sich auch jemand anders genauer.

This is the English equivalent (it's in Leo), I don' t remember any previous discussion, try an archive search.

I think you can use "to put the cart before the horse" if you specifically mean doing something first that should (logically) not be done till later, but not necessarily with the implication of ending up with a complete mess.

There is considerable overlap, but if you mean "eine Sache ganz verkehrt angehen" [Duden 11], "to go about it [or things] the wrong way" might be preferable.

Thanks, Mike needed your thoughtful input otherwise I would have ended up with a mess