The site Women’s Memoirs is offering a free 22-page book, Journaling Essentials: Everything You Need to Know to Start by Amber Lea Starfire.
Here’s what’s in the guide includes: 
Seven Wonderful Benefits of Journaling: Each benefit comes with an exercise and space to conduct the exercise. The benefits Starfire discusses are:
- Self-Care
- Catharsisand Emotional Healing
- Clarity
- Making Meaning of the Meaningless
- Personal Growth
- Holding Onto Memories
- Sharing Memories: Writing for Others
- Enhanced Creativity
Starfire offers chapters on Getting Started and Staying Started, with exercises for both, along with a piece called Schedule a Time Just for YOU.
Noting that there are really no rules, just guidelines, she offers guidelines in a chapter called Rules of Journal Writing.
My favorite chapter includes 20 Writing Prompts and also offers Inspirational Quotes
Finally, Starfire provides a small collection of links to The Journal Writing Community.
Download the guide here. (Look for a box with the book cover on the right side of the page; enter your name and e-mail address to download the PDF.)