Basically, you need to know a variety of styles. Excellent sight-reading is an absolute must. (sometimes from handwritten notes)... and improvisation is needed all the time.
In order to get work you need to live in a city where the jobs are available. ie, no point living in buttcreak, MA if all the work is in L.A.
Reliable transportation and messaging service.
Excellent equipment and a variety of guitars/amps/pedals to work with. Secondary instruments like Ukelele/banjo can make you extra money cause union rules say you have to be paid per instrument.
The ability to not be an ass and follow directions.. especially when you first start out. ie, don't act like you know everything or the older players will get you.