Watch some youtube videos. No, really. Just do a google search for something like "art journal techniques youtube". It will give you lots of fun and interesting videos. I can never sit and watch them without immediately wanting to try some of the tricks and products they use! And don't feel that you can't watch the videos without first HAVING the materials... many feature stuff you've just got lying around your house to begin with :)
Flip through a magazine. ANY magazine. You will inevitably see something that will spark an idea in you. And go with it! Let that idea blossom into your own creativity. For example, if you flip through the magazine and see a city skyline at sunset, you may think it would make a very pretty journal page, but you can't draw a city. So? You can cut out different patterns to make various sized rectangles to represent the city buildings. See? One of the best things of creating in your journal is you can be inspired by something, but that is just a spring board... when you create, you totally make it your own! Let it grow :)
Listen to music. Pay attention to the words. You'll likely be brought back to a certain time, or the lyrics may cause you to think of a person. Let's say you hear a verse that reminds you of your ex-friend. Or your Grandmother. So concentrate on the thoughts of your Grandmother. Maybe you'll remember games she'd play with you, or that brooch she wore on her sweater ever day. Sketch that brooch. Doodle around it, or add magazine clippings, of cupcakes, or cookies, like those she'd used to bake for you. The possibilities are endless!
Another thing you can do is just start sketching shapes. Circles... squares... triangles... whatever your heart desires. Try different colors. Make some bold lines, and some thin. Maybe make one line of dots or dashes. Add some words, if you prefer. "Hope". "Grow". "Fly". Go with it! Have hope, now grow, and get flying!