I would say develop a unique passion. Are you a senior, though? It might be too late to do that. But if you're going to have scores/GPA on the lower end of the spectrum, the only thing that could possibly get you in would be to have cultivated a long-term, passionate EC or two. It looks like it might be too late though.
But maybe you're passionate about tutoring kids or being in the orchestra. These aren't very unique EC's, though, so I'm not sure if it'd help you...Is there anything else you're passionate about?