Eli,
You're opening a big can of worms here ... there are many skills ... questioning skills, listening skills, presenting skills, closing skills, product knowledge, prospecting skills, positioning, pre-call planning, etc. I would suggest the most important skill(s) is asking targeted questions and listening. When you break sales down to a common denominator it's all about asking the right questions to determine the pain your prospect(s) are experiencing and then presenting your product or service as a solution to help them solve their pain in such a way that they can see, hear and feel the solution.
I would sugges the book Sales Techiques by Bill Brooks as a good read about a simple selling process. It covers all aspects of his selling system designed to keep you, the sales professional, in control of the sale.
Good luck,
Steve