Much advice about both writing about art, and academic writing in general, is free online. These sites need evaluating carefully, but some are very good, for instance:
Academic Phrasebank
From the University of Manchester. An excellent guide to the elements of academic style.
Essay guides from the University of Manchester
Punctuation
A guide from the University of Sussex.
Quoting and Paraphrasing
From the University of Wisconsin. Useful if you are not sure if are at risk of plagiarising; please do also seek guidance from SIA faculty in this situation.
Speaking in Academic Contexts
Advice for seminars, presentations and group work.
Using English for Academic Purposes for Students in Higher Education
Comprehensive guide by English language and educational consultant Andy Gillett.
The key section of the book section is:
But see also: