There are many kinds of journals. Some people record their innermost thoughts and feelings daily. Others write a single poem or a few lines of an essay once a week, every few months, or simply "whenever". The wonderful thing about journaling is that there are no rules or restrictions. To get your creative juices flowing, start a journal to record inspirational thoughts and ideas, or keep track of an artistic project. Choose a blank book, preferably without lines, that appeals to you in color, size, and texture. Or make your own journal, designing a cover with drawings and photographs. Starting is the most important action. In the beginning, you might want to schedule journal time into your day... but even if you don't, you know it is there waiting for you when inspiration strikes.
One of the best ways to encourage creativity is to try new things. Don't let your preconceived notions of what a "journal" should be get in your way. Anything too formal or linear is up for grabs when flying with your creativity: write with your non-dominant hand, or write in a different direction - landscape orientation is a great start, diagonally, or even in a circle. When it comes down to it, you don't even really need to write any words at all: draw, doodle, or paste a collage of images instead. The important thing is not to worry about your artistic skill in creating the journal, but to focus instead on your own expression. Anything fresh will do to kick-start your creativity: use different colored pens or pencils; fill your pages with colorful doodles; anything to keep you from traveling the same worn paths in your thinking.
Your journal can be about any aspect of your creativity. You may or may not believe it at this moment, but there is no such thing as a "non-creative person". Any collection of fragments can be your repository of dreams, your prompt book for brilliant ideas, or the start of a larger creative endeavor. Don't just spend time putting a journal together; every once in a while, take it down off the shelf and read it as if you just found someone else's journal lying there (and that it was okay to look inside). The inspiration you discover may surprise you.