This isn't going to work for everyone but it's worth a try! You can write things down like your dreams and future ambitions and explain them, this could be done when you're feeling low and can make you so much happier and upbeat. I write these articles to make me feel happier and also just because I find it useful writing my feelings and opinions down as it helps me to understand myself, my views and I can compare this with other people's views or my view a few months later to see if it has changed.
All you need is a cheap book/notepad and a pen. Its a really worthwhile thing to do and well worth a go!