Before you can create a stunning portfolio or market yourself to companies as a technical writing intern, you need some grounding in the basics.
If you're in a college that offers a degree in technical writing (usually a degree in English with an emphasis in technical writing), by all means do it.
If I were doing it over, I would actually double-major in English and computer science. Some students prefer to get domain knowledge, such as in accounting or engineering, and then supplement that knowledge with writing skills.
Whatever your situation, learn the basics of technical communication. For starters, learn how to write well. Learn grammar. Learn to analyze an audience, create personas, approach documentation from a task-oriented perspective.
Learn to number your steps, keep your topic titles parallel, and be brief and concise. Learn to write useful instructions rather than obvious statements. Learn when to use screenshots and when to omit them. Learn the strengths and weaknesses of different help formats, such as wikis versus quick reference guides versus video tutorials. You can't do anything without first grounding yourself in the fundamentals.
You may not learn all of these concepts in your program. If not, you can supplement your program with some instruction from professionals in the field. The Society for Technical Communication (STC) has an excellent certification course from well-known professionals. You can also read the Intercom and Technical Communication Journal.
If you don't have money to join the STC, connect with someone who is a member and ask to borrow back issues. Read blogs and books published by professionals in the field (here's a list of foundation books). However you do it, get a solid education. This is critical before you can move forward.
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I'm a technical writer based in the California San Francisco Bay area. Topics I write about on this blog include technical writing, authoring and publishing tools, API documentation, tech comm trends, visual communication, technical writing career advice, information architecture and findability, developer documentation, and more. If you're a professional or aspiring technical writer, be sure to subscribe to email updates using the form above. You can learn more about me here. You can also contact me with questions.