When my students get the hang of these techniques, it makes an enormous difference to their creative writing - but these things take practice.
These tips (which I wrote in reply to a customer's question) build on some remarks towards the end of another blog post about 11 plus preparation.
Before you write - before you plan - take a little time to daydream. If you can see your story's world in your head, you will be able to describe it powerfully. If you can't, your descriptions risk being superficial.
Keep things simple: stick to one main plot event, and focus on bringing it to life. If there are too many things happening, your descriptive skills may get lost.
Similarly, it is usually best to focus on one character.
Put a little dialogue in, but avoid writing a play script! Describe how people move around between saying things, the expressions on their faces, and so on.
Short stories don't need an introduction.
Show, don't tell: rather than "Simon looked up. He was angry," write "As Simon looked up I could see the flexing of his jaw muscles."
Use a range of senses throughout. If you use only visual descriptions, you are asking the reader to enter your world as a person who is deaf, cannot taste or smell, and experiences no physical feelings.
Sometimes describe things using a sense other than the most obvious one. Instead of "It was a cold morning," write "I could hear the crackling of thawing ice on the windscreens."
Similes and metaphors are useful (and can be impressive), but they have to make things clearer for the reader, not create confusion. "He won the sprint like a racing car" asks more questions than it answers. Was he noisy? Was he travelling at 150 miles per hour? On the other hand, "He ducked his head and slipped across the line as cleanly as a racing car" helps me to picture the event exactly as intended.
Suspense is good if it is appropriate to the story, but don't jack-knife it in clumsily. "Or was it ... ?" doesn't make me any more curious than I was before. If you write in a way that builds suspense, this will speak for itself; but not every story needs it, and it is certainly not true that every story needs to involve a cliff-hanger.