I'm currently working on a book for other siblings affected by the loss of a sibling due to a tragedy. While I am not working on my first book I have a couple devotionals I putter around with. I used to write in my journal daily but that has gone on the wayside - praying to get back into the habit while also working on my writing for publication.
I start and end my writing time with prayer. I have found when I "rush" to write, nothing comes yet when I spend time in prayer and ask for God's guidance, wording and strength ~ my writing sessions are much smoother and more productive. I encourage you to do the same, invite God into your heart and mind before you start writing and thank him when you end.
Grab your journal, a pencil or pen and your Bible and spend some time praying and writing! If you are stuck on what to write about the first few times, try writing about "My most memorable VBS (Vacation Bible School) experience" or "I never went to VBS because..." Be creative and write about what you know...you'll be surprised!