Keeping up with your writing is key. The best way to do this is to make it a part of your daily routine. Some people write just before going to sleep, others right after dinner. Whenever you choose to write, stick to it and focus solely on writing for a set period of time.
There's no set rules about what constitutes a journal. If you want to write a poem in place of a detailed explanation of your day, go for it. If you want your journal to only address your dreams, your love life or your travel aspirations, that's fair game too.
Blogs are the new journal. With so many blogging communities available, it may help some younger writers to keep a public journal that they can share. This might not be everyone's cup of tea, but if you feel more productive behind a keyboard than with a pen and a notebook, it's worth a try.
Mementos from your day can be a fun addition to your journal entries. A flyer from a concert, a playbill from a show, a photo of a friend or a matchbook cover all fit in between your pages and act as visual aides to help tell your story.