Embrace a theatrical element for your story and commit to it. To start, take a close look at theatrical traditions and be willing to put these ideas to use in your story.
For instance, a villain in a play might be signified by a physical trait like a garish mustache. This is a simple way for the audience to identify that character on stage as the bad guy, and the same principle will work for your written work. If handled correctly, whenever this character is being depicted and emphasis is brought to his cruel face and accompanying facial hair, it can then be written that all facial hair or body hair in general can be connected to the feelings of dread and discomfort invoked by this character. Try it out and play with this idea, done right it can add to the tale.
Associate and use clothing or colors with a particular character, and this too will become symbolic and add resonance. In the same way that the previous mustache example might work for the antagonist, try using wardrobe or color in an identical fashion. If you call attention to a sympathetic character's fingerless gloves and then repeat images and themes connected to those gloves, then the character will be invoked easily and can summon emotion from subtle suggestion. This device, again made popular in theater, can apply to literature as well and is worth a lot of experimenting in early drafts of your story until you get it down right.
Study up on archetypes and apply what you learn of them to your story. Essentially, archetypes are familiar models and character templates recognizable all over. What is so telling and true of archetypes is that they exist in cultures across the globe and are universal. It would be wise to weave in elements of your favorite archetypes to your story, and the symbolism attached to them and the familiarity they have will strengthen and legitimize your story. Some archetypes you are probably already familiar with include the perpetual child (Peter Pan), the star-crossed lovers (Romeo and Juliet), the trickster (Loki, Harpo Marx), the wise old man (Gandalf, Obi-Wan Kenobi) and on and on. It is probable that whatever stories appeal to you the most are flush with archetypal characters. The psychoanalyst Carl Jung made great strides in categorizing and detailing universal archetypes, and American lecturer, mythologist and writer Joseph Campbell similarly made much out of archetypes. Both Jung and Campbell offer a wealth of knowledge on the subject, and their works are populated with them and are worth studying for any writer serious about symbolism in literature.
Write assertively and clearly so that the symbols stand out. In the same way that your dreams can seem vivid and meaningful, treat the fictional world of your story this way, too. When writing symbolically your story should contain elements of magical realism so that your audience knows that is part of the story. For this reason your consistent writing will build to the believability of the world you are creating. This style of writing may not come easy at first, but if you want your writing to be rife with symbolism you should be prepared to rewrite and rework your story until it all clicks.
Create your own symbols and your own cosmology and apply this to your story. As the storyteller you are essentially God to your creation, and the symbols you create hold whatever meaning you choose to apply to it. This is something that you may not feel confident enough to do at first, depending on how much writing you do, but you hold all the cards when you are telling a story and this is empowering. As your confidence builds so to can your cosmology. The 18th century English poet and painter William Blake, famous for his distinctive body of work, created his own cosmology and helped to define the Romantic era. More recently, in the last century, American writer H.P. Lovecraft created his own cosmology for his eerie supernatural stories and novels. Both Blake and Lovecraft, working to different ends and different themes, are connected by their distinct and strong visions, which were different from their contemporaries. What, as writers, is important to glean from these men is that writers establish the worlds they write in; in the fantasy genre this is done all the time. Be bold and be daring in your use of symbolism, and anything that does not work can easily be snipped out.
Use the right symbols for your story. If your story is set in a religious or spiritual backdrop, then it is assured that there will be an abundance of symbolism at your disposal. All the world's religions use symbolism and symbolic gestures, such as the Christian use of bread and wine as figurative symbols of Christ's flesh and blood.
Use the sun as a symbol. One of the most powerful symbols known to us is the sun, and solar imagery dominates many aspects of our culture. Not just in our religions but in our psychology, astrology, mythology and in mysticism. There are many ways such symbolism can be effectively used in your story depending on the nature of your tale.
Rely on numbers to act as symbols, too, and even more depth and understanding can be added to your work. Numerals are symbols for the numbers they represent and this is worth throwing into the literary stew you are concocting as an added spice. Many people associate the number 13, for instance, with bad luck, and it is a popular belief that a clover with four leaves is lucky and that seven is also a good fortune numeral. Play on these notions and use them accordingly in your writing.
Combine ideas of astrology into what you are writing. Granted, this may not work for everything you scribe, but since astrology is rich in imagery and is recognized globally you stand to strengthen the appeal of your story by using astrological symbols or emphasizing certain aspects of it. Astrology's zodiac signs, for example, are not just familiar to Westerners, but also to Chinese, Islamic and Hindu traditions as well as psychology and the art world in general.
Research and study up on symbols and keep learning. The more you learn the better equipped you will become at inserting powerful symbols into your work. A good place to look deep into symbolism, apart from the literature section at your local library, is to visit the cinema. The most skilled filmmakers and the most artistic express themselves in images and use a grammar rich in this to articulate their visions. Innovators in this area working in film include the German Expressionists like Fritz Lang ("M," "Metropolis"), F.W. Murnau ("Nosferatu," "Sunrise") and others like Orson Wells ("Citizen Kane," "Touch of Evil") and Alfred Hitchcock ("Rear Window," "Vertigo"). These filmmakers and scores more like them used literary devices and strong symbolic images to propel their stories forward, and there is much to be gained from viewing their masterpieces and using similar motifs in your own work.