These are a few ideas that keep surfacing every time I hear smart/accomplished people talk or observe smart/accomplished people work. This is applicable to all folks who are trying to break into the entertainment industry.

1. Create. Write. For all the aforementioned reasons and also: JUST DO IT! 
   If you're into multi-cam sitcoms, watch those obsessively and break them down into pieces, find the structure. If you're into hour long political dramas a la Aaron Sorkin, watch those obsessively and find the structure in the episodes. If you're into dramatic plays, ensemble plays, whatever it is: consume them, observe them, break them down, put them back together again. It'll make you a better actor, writer, director, creator, whatever!
2. Work begets work. 
   To get that next job, you must work hard now. To get that first job, see #1. It might not be creatively fulfilling work, but it will keep you working and if you're trying to establish a career, these links matter. If getting that first job is too hard, make that first job. (Write that spec, put up that one man show, join that Improv class, produce that play, tape that web series.)
3. Find your people.
   No matter where you are, find your people. Find the people who want to create the same things as you: TV? Films? Theatre? Musicals? Comedies? Sketch? Improv? Find these people. You will teach each other, grow together, and create together.
4. Don't show up empty handed.
   When you find your people or when searching for your people, you'll want to have something to bring to the table. That's why #1 and #2 are so important. Plus, a great bonus for following #1 and #2: it keeps bullshit thoughts like "Why haven't I made it yet?" and "Why is this so hard?" and "Where is the pizza?" at bay. The power to create--the thing we claim we want so badly to do--is in our hands.
5. It's about stamina.
   I've heard a lot of people say "If there's anything, anything else you'd rather be doing in the world, go do that. This business is so, so, so hard and there's no guarantee that it will pay off." My professor and mentor framed it in a way I think is more digestible: "Do you still have the stamina for it?" Given all the shitty jobs you've taken on, the sacrifices you've made, that extra major you took on at college but have never used in a work setting--is it still worth it? If the answer is yes, carry on my wayward son and fight the good fight! Because there are a million things you could be doing, but you chose to do this. And remember: #'s 1 and 2 will keep you falling in love with the work, which will only help you persevere.