The best tool at an aspiring writer's disposal is a journal. Electronic or paper, whatever. Write about your day, express your feelings, complain about the jerk who cut you off in traffic. Write down ideas as they come, brainstorm for something you're currently writing, create simple poetry. Write short stories, complete writing exercises, describe that character or scene you just can't get out of your head. It doesn't matter what you write, just that you write. Pick a certain time of the day and write as little or as much as you like but make sure that you write consistently.
I have a notebook at work and at home, but I also use features on my iPhone when I don't have a pen or have a thought I'd like to remember later. My tendency to think of things when lying in bed at night has made this essential; after all, I can't write very legibly without a light (especially if it's long), so my phone is the perfect solution. I cannot begin to count the number of ideas, sentences, characters, etc, that were lost due to the dark midnight hour. What can I say? My muse is a night owl!
When you get to the point that you're writing creatively on a daily basis, I suggest "upgrading" to a writer's journal. While there's no requirement to completely abandon the original journal, a writer's journal is important because it focuses on what you're writing. Specifically, it provides a special place to document your journey and keep ideas, notes, and research that you can refer to as long as you write. Explore thoughts and feelings related to characters, scenes, or plots. React to your own work. Flesh out histories, settings, or descriptions. Create a journal entry as the character you're working on. Make notes on where to pick up tomorrow. Ultimately, the way you use your writing journal is up to you. Use it to the fullest extent because you never know when something old might complement and infuse energy into something new.