Do you have any people skills? by that, i mean have you ever sold things? first off...know your items. Have as much knowledge as you can. or know how to find out.
second. Always be courteous. People will ask and demand the stupidest things, but keep a smile on your face at all times. Learn to write e-mails that are short but to the point.
Thirdly: Have a pleasant phone voice. Always be at least a bit cheery, not a grump. In all my years of sales, those that have the attitude do the best. People forgive alot but not a bad attitude.
Just be sure to know your product, have all information at your fingertips and be pleasant. That's about it.