How you approach English Language Arts depends on your homeschooling methods. If you are Unschooling then this may be entirely optional. If you are doing some type of academic learning, then there may be some structure and curriculum involved.
Once your student has the basics of reading and writing, it may make sense to focus more on real life skills such as:
Business writing (email conventions, articles, promotions, forms, news articles, reports)
Business communication (social conventions, listening skills, presentations, group meetings)
Rhetoric (persuasion, analyzing speeches, debate and civil argument)
News Analysis (current events article comparisons, bias, misleading headlines, reliable sources)
A typical high school English class has several "units" focusing on different literature forms, writing assignments, and discussions. Vocabulary and grammar may still be addressed occasionally. If your ASD teen still struggles with writing, this is the time to refine those skills.
Read a fiction book: Assign a few chapters at a time, discuss verbally or analyze in writing (characters, setting, plot, theme). If you need ideas, try the GoodReads 10th Grade Reading List. Or for a more modern selection, the Barnes and Noble Teens Bestsellers.
Book Study materials: A great place for literature resources is TeachersPayTeachers. Search for "unit study" on the book you chose. They will have inexpensive packets of worksheets or project ideas.
Film analysis: Watch a few movies in a genre and discuss the acting, historical aspects, camera work, dialog, etc. Read professional movie reviews and then write your own.
Short story unit: Stories from a literature textbook or online sources. Short stories are quick while offering an unusual perspective.
Shakespeare? If your teen has strong verbal skills. Reading out loud back and forth makes it fun, with some quiz questions for each Act (many sources online).
Summarizing: (a difficult skill for many ASD kids), subscribe to a news outlet such as BBC, read an article of their choosing and summarize in one paragraph.
Grammar brush up: Get the workbook, Editor in Chief, Level 3. Do one or two pages a day, finding the errors.
Touch Typing: If they haven't learned to type by now, this is the time!
If putting together your own English study is daunting, try an online class or prepared curriculum. Some ideas:
Bravewriter has many writing classes, for creative writing, essays, and journaling. Made for those who need some extra help and feedback from a pro.
Home2Teach has writing classes as well, with much more hands-on teacher input
FishTank has free ELA lesson content that you can use at your own pace
For more resources and ideas, see the Curriculum Pages.