1st years cannot apply for a TA position within TFT, but you may apply to TA in other departments (English, Humanities, etc.).
A few teaching assistant positions are offered to Screenwriting students.
Since events like Showcase are student-driven, the faculty also seems likely to reward those who rank among the most active. TAs are not only paid a salary, but, as university employees, also benefit from registration fee waivers and paid medical insurance.
Furthermore, unlike Work Study, administered by the Financial Aid office, Teaching Assistantships offer academic experience specific to our field of interest, rather than clerical or service work elsewhere in the university.
TIP: Depending on your undergraduate work, language skills, etc., you might consider looking elsewhere in the university, like the Classics or English departments, for a TA position. A number of Screenwriters have been successful in doing so.
If you want to TA in the English Department, specifically Composition (a required freshman course), there are several positions and they frequently accept non-English Department grad students. HOWEVER, you must take the class "495: Teaching Composition" before becoming a TA for the English Department. That class is generally offered in the Fall and Spring quarters. You will have to email the department and ask for a PTE number.
TAs need to be aware of the 12 units needed to receive financial aid. A 50% TAship translates into 4 units, but there are others that fall below that percentage and only count for 2 units.