Look at a basic job description:

Library Assistant Job Description, Duties and Jobs - Part 1

Library Assistant: Employment Info and Requirements for Becoming a Library Assistant

and take courses that would give you those skills and education.

I applied for a library assistant job once and the interviewed asked about the last couple books I had read, their titles and authors and why I read those books, what I learned from them and what they were "about" (I had to give a synopsis). So, I'd certainly do my English studies and pay attention to why I wanted to work in a library other than "I really like books/to read", I'd go into more detail with myself about my reading.