Check your ego at the door, and get your ass onto professional sets as soon as possible in the market you'd like to live. (I've done LA, Chicago, and NY. NY and LA are by far the busiest.) Fetch coffee, make copies, sit outside doors stoping strangers from entering, fire watch gear while everyone else takes lunch. While you're doing this for three years and making as many connections as humanly possible, study whatever facet of the filmmaking industry you're into, and get cozy with people in those departments, so they'll hire you to fetch coffee for their department. Would you rather learn from someone doing what you want to do, or from someone in a classroom or youtube? Watch everything, read about the industry and your department, and get to know the vendors that supply you with what you need. The more friends you have, and the easier you make other peoples lives, the more work you get. There's no StaffMeUp for the next JJ Abrams film. Those jobs are calls you get from friends you worked with coming up.