Advice for professional development

I am working currently in a position which has me writing web applications using PHP primarily. I have no issue with completing the majority of my projects here and have generally done well since i started (this is my first software dev job after a long period of time in general IT).

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I've found, though, that I work much better with c# and would like to look into making the move to a position which would utilize this. What, if any, skills should I try to add to my resume before making the jump in order to be taken seriously by prospective employers?