Some television writers "make it" by working at the local Starbucks and spending their evening working on their latest spec script; this is definitely one option. However, there are several viable alternatives. And although it's nearly impossible to pick the perfect path to any desired job in the entertainment industry, here are three of the most common ones:
If you want to work in television it's always a good idea to get a job on a show. One of the only entry-level jobs is a PA. Being around the production gives you the opportunity to get to know the process, and gives you great exposure to people.
If you're a PA on a show and your ultimate goal is to write, then be certain to read all the scripts. Every day a script is rewritten or issued. Read every first draft revision and re-write. This will give you a better understanding of the process and the need to re-write.
Most shows will have a PA position in the writer offices. This person will primarily be responsible for taking care of the writers' needs: getting lunch, coffee, script distribution. This is a great place to observe the writing process first hand. It's also an ideal position for networking with writers. In this position you'll have access to all script aspects. You'll hear early story ideas, see beat sheets, outlines and numerous drafts long before they're considered for production.
There's no better place for a young writer than in the writer's room. As a writer's assistant you'll be surrounded by writing all day, every day. Not only are you an instrumental part of the script process, but eventually you may be given an opportunity to write an episode or pitch an idea for the show. Be careful though; it's very important to understand your place in this process.