Keep a dream journal. If you want to tap in to your dreams and use them for creative purposes, you must record them. How many times have you awoken from a dream and clearly recalled it only to have forget it later? The only way to keep track of your dreams and to recall them with any level of accuracy is to write them all down.
Have a pen and paper near your bed. If you awake in the middle of the night or in the morning only to discover you can't recall very much, write out whatever you can. If you can only recall a feeling or a certain image, write that down. You may find that jotting down a quick line or two may be enough for you to recall the entire dream and more.
It is not enough to awaken and tell yourself you will remember this dream. This is hardly ever the case. Most people may recall one or two dreams in a week, but a devoted dream diarist will be able to recall dozens in the same allotted time. And the more you journal your dreams the more creative connections you will make. You will start to notice reoccurring motifs, characters, locations and situations.
Study artists and writers who have been affected by dreams. There are many great artists who have been influenced by their dreams and you can learn a great deal by pursuing their work and observing how they have incorporated their dreams into their milieu.
Salvador Dali, for instance, painted and wrote about his dreams and even made two classic surrealist films with one of his greatest collaborators, Louis Buñuel. These films, "L'Âge d'Or" and "Un Chien Andalou" incorporate dream logic and imagery in an artistic and inspiring fashion and are worth repeated viewings.
Many writers use dreams directly in their work and write on the subject at length. Carlos Castaneda's novels, particularly the Don Juan titles, concern themselves with dreams and describe techniques on lucid dreaming and creativity in ways that will help both writers and artists to be inspired by them. Similarly the great Beat Generation writer, William S. Burroughs was an avid dream diarist and all of his novels incorporate dream imagery and logic. He derived his novel "My Education: A Book of Dreams" entirely from his dream journals. The story is a powerful and haunting testimony to the creative powers dreams hold.
Other writers such as Jorge Luis Borges, Richard Brautigan, Italo Calvino, Philip K. Dick, Ursula Le Guin, Doris Lessing and Gabriel Garcia Marquez have all written or write in a magical realist style influenced by their dreams. It is well worth it to read some or all of these authors and see how dreaming has influenced their work.
Apply what you have learned about dreams. You've been keeping a dream diary, and maybe you have also been doing some lucid dreaming experiments (many of which are detailed in both Burroughs' and Castaneda's writings) and are ready to apply some of this material to your own writing. Start letting images and situations from your dream journals seep in to your novel, short stories or poetry. There are really no hard and fast rules here, and an effective way to let your dreams influence your work is to let its imagery and emotions appear in your story. Use your dream ideas to add color and depth to your tale gradually at first. Maybe your protagonist is haunted by dream scenarios or dream-like feelings that propel the story forward. You have to use your own discretion but don't be afraid to let your writing follow dream-like logic, knowing that you might later have to edit it down to follow whatever reality you have established in your novel.
Let the dreamy aspect of your novel guide the writing but not overcome it. If your novel is very poetic and experimental, you can incorporate as much dream imagery as you want, but if you're writing a more realistic piece, then a sudden shift into dreams might read as forced or contrived and alienate your potential audience. So, use your own judgment and avoid cliché as much as possible. Nothing infuriates a reader more than the "it was all a dream" finish, unless there is a new wrinkle in it or it's to serve a specific purpose.
Write assertively, and your work will be all the stronger for it. If you find you are at an impasse with your writing and out of ideas or you're feeling a little exhausted, take a break. Explore your dream journals and read up on dreams to further empower yourself. The more you know about dreams the more free-flowing and informed you stand to be in expressing them. Because so many theories exist around dreams and their interpretations, it is worth researching lots of views on them and using various ideas about them in your work.
Remain open to change and going in unexpected directions. It's a mistake to settle on any one way of thinking on a subject. Just as the characters and story threads in your novel can have an infinite number of resolutions, so to can dreams have an infinite number of meanings. Keep learning about them and allow your writing process and dream inspirations to be malleable.