Be a keen watcher. Be a sponge. Scan the people and the animals around you for gestures, expressions, habits, poses. Once you've honed your personal second nature for seeing, expand your sensory collection to your other four senses: hearing, feeling, smelling and tasting. Hear the unique inflections, patterns and dialogue in the conversations around you; feel the intoxicating plethora of tactile sensations during love-making; smell the evening jasmine in your father's garden; taste the grit of a desert sandstorm. All of these sensations, so many and so varied, are an invaluable cache of experiential fodder from which to build a richness of description into your writing. They provide a linguistic superstructure that bestows a three-dimensional reality to your scenes. They inform and influence everything in the composition of your fiction from dialogue to character to setting. In short, they are an essential component to giving your readers a convincing, emotionally engaging, full-fledged experience of the events in your narrative, a potent means through which to help your readers meet your characters.
Keep in mind, writing fiction is truly a creative process. Don't limit yourself to just reporting your collected experiences. Throw them into a box, shake the box around and see what kinds of interesting and contextually appropriate new syntheses you can form. I had a vignette where a character was surprised and bewildered. The second sentence in the scene is: "Crashing cymbals of bright radiance clanged before his eyes." Radiance is seen. Clangs are heard. Yet the dazed character "sees" the clang of cymbals. The discordant merging of sensory experience conveys the disorientation intrinsic to the vignette and it gives your readers an interesting, multi-sensory image to consider.
OK. I've made the case that your five mortal senses will give you more than enough material with which to weave a rich tapestry of description into the fabric of your stories.
But there's a sixth sense.
Strictly linear thinkers need not read further. Skip to the next post. The rest of you, please come this way...oh, and watch the little, dancing wood nymphs around your feet, young man. They're fragile and they don't appreciate being stepped on.
I've felt and experienced sensations beyond the traditional five senses. If any of you have "seen" inside the psychology of strangers walking past you at the mall or heard your pet's thoughts or watched a window shatter before your eyes for no reason or felt an empty kitchen blow dry, frigid air onto the back of your neck in the quiet stillness of a bright winter day, then you know what I mean. Unless one of these experiences is deeply personal or has an essentially private nature, consider including a description of it in your fiction. There's a first-person description of the afterlife in one of my novels. Yes, the novel's fiction. But almost the entirety of that vision is someone's actual experience.
Use your senses as a tool for creative writing...use all six of them.