
SRLN Brief: Plain Language Audit Tools for Your Documents (SRLN 2015)
Here are various resources to help test your documents:

Article: Focus Group: Connecting Writers of Legal Documents with Their Audience (Mindlin & McCormick 2012)
This article is about focus groups which are a qualitative research tool that tell you if the main message and purpose of your form are understood.

Article: Appellate Practice — Including Legal Writing from a Judge’s Perspective (Painter 2000)
The article, Appellate Practice–Including Legal Writing From a Judge's Perspective, is mainly about the important attributes of briefs to help in persuading a court.

Article: Legal Writing 201: 30 Suggestions to Improve Readability (Painter 2002)
This articles cites several suggestions on how to make legal documents clearer and easier to read.
Resource: Scribes Journal of Legal Writing (American Society of Legal Writers)
The Scribes Journal of Legal Writing is a a scholarly journal which publishes articles about legal writing. It has published articles by many of the best-known figures in legal writing — including Garner, Kimble, Charles Alan Wright, Richard Posne
Handbook: Plain Language (Lauchman 2009)
This handbook is intended for the writers in the U.S. federal government. It focuses on aspects of writing that are especially important to Plain Language.

Article: Plain Language in Law (Dave 2002)
Plain Language in Law, by Sandeep Dave cites several resources about using plain language in legal documents.

Article: Lower-Literacy Users: Writing for a Broad Consumer Audience (Nielsen 2005)
The article, Lower-Literacy Users: Writing for a Broad Consumer Audience, is about the research on lower-literacy usability of documents or texts on websites.
Handbook: Write For Your Reader (NWT Literacy Council 2015)
This is an easy-to-use 'how to' manual for people who write or edit reports, memos, minutes, brochures, or other documents.

Article: A Modest Wish List for Legal Writing (Kimble 2000)
The author of A Modest Wish List for Legal Writing, Joseph Kimble, cited some ways to improve the readabilty of legal documents.