Include the date on the morning of a dream. Patricia Garfield suggests that before you turn out the lights at night, "...jot down what you have done and felt during the day. This paragraph of 'facts' needn't be long but should include the salient events and emotions you experienced. This may hardly seem necessary but two months or two years from now you will find it invaluable.
I know someone who keeps a dream journal in his computer. He takes advantage of different fonts and spacing and includes plenty of colorful graphics. The result is a beautiful document several hundred pages long. Keeping a journal in your computer also gives you the advantage of very easily looking up what certain images mean to you. You can create your own personal dictionary. By hitting "find" on the keyboard, you can see where and how a certain metaphor or symbol was used.