Pre season, do preseason work, but start vaulting early, esp. Distance vault from 3-4 strides, work your way back and up poles. I could go on and on, but those four, I wouldn't want to do with-out, as coach or athlete. Wide is generally easier to bend a pole with, but it prevents the chest from coming through as well. Narrow makes the top easier and facilitates opening the chest.
Comfort is important, but stay on the narrow side.
Hold low until you improve your tech. Have a coach that knows what he's saying, and learn about it yourself to make sure. Hold low till you get the tech.