1 - Notebook (cheap is the best)
1 - Pen
1 - Journal (Your preference here of either something more durable than the notebook, another notebook, the same notebook, or perhaps a digital document.)
Step 1: Preparation
Before falling asleep:
Open the notebook to a blank page and set it in a place you can easily remember and reach without opening your eyes. Place the pen in an equally memorable and accessible location but separate it from the notebook to avoid accidentally dropping the pen. Keeping these items separate highly reduces my stress of losing the pen, thus freeing my mind for dream recall.
Make sure to check the ink in your pen regularly. Once, after writing down a dream, I opened my eyes to see what I wrote and saw nothing but blank pages. The ink in my pen ran out! Prevent this situation by checking the pen's ink during the day every once in a while, depending on use. Also, try to write with the pen tip facing down, unless you have a pen that can write in any position. Some pens stop inking after a few words when not in the correct position and in such a situation you'll end up with blank dreams! Preparation, aside from experience, could be done by lying in bed and testing where it's most comfortable to hold the notebook and pen and testing to see if the pen works in such positions.