Since I'm a technophile, my journal is completely digital. I use Red Notebook for its calendar, search options and word cloud. Instead of flipping through pages, looking for something I wrote I don't know when, I can type a few words in the search box and voila..there's what I was trying to find out.
My journal helps me decide what to discuss with Steve, and what to keep to myself. For example, it helps me figure out if a bout of depression is a short term thing or if has been going on for some time. Often, bipolar individuals do not know when they are experiencing a depressive episode until they are deep within it. If it seems like things have been going on for some time, I can look back and see what I've written in my journal.
My journal keeps me on a positive track. I can always tell when I'm starting to become negative about things because my word cloud shows the negative words like "can't," "don't," "overwhelmed" and "sad" in great big letters. I don't edit my journal entries to make them happier, but I'm more aware of my thinking. Just that little visual reminder tells me that I should start focusing the things I'm grateful for, rather than the things that bring me down.
Finally, like all journals, it is a place where I can vent and scream and cry without anyone knowing about it. Sometimes, just writing about a situation is all I need to make it better. I don't have to be "perfect" or "upbeat" or even understanding. I just write what is inside of me.
I wake up early every morning specifically to write in my journal. I prefer the mornings because venting my anger and frustration early keeps me from having a bad day. It works the same when I write about what I'm grateful for. It's kind of hard to be cranky when you've just spent a half hour expressing gratitude for the sunrise.
If you don't have a journal, I highly recommend it. It can be as little as a single sentence like the one Gretchen at The Happiness Project keeps. Everyone needs a place where they can express their feelings with no repercussions.