The following e-books are OER and free to access/use.
College Success (concise edition)
College Success (full edition)
This book is aimed at high school students, but I've found that it explains a few things better than the standard College Success ebook.
Most websites on body doubling are framed around ADHD, but this is a strategy that can help anyone.
Tips & Tools from The Writing Center at the University of North Carolina at Chapel Hill