Great Question: Although the number of skills needed to succeed as a marketer can be quite lengthy and varied depending on one's specific goals, the first thing I personally would mention is that of
1. PRODUCT OR INFORMATION SELECTION.
After all, what is the use of marketing anything if it isn't of value to those seeing it. Of course, knowing the basic functions of today's technologies will definitely serve anyone well in today's internet world.
Who Are You? People want to feel some sort of positive connection with someone trying to present them with an offer. Your approach will definitely be something that will go a long way towards a marketers over-all success weather this be in personal communicating or even letting your personality shine through in your writing style.
As I stated in the beginning, this list could go on and on but these are two that I think will serve any marketer well.