Show, don't tell.
How many times have you heard that phrase? A million? A zillion? A quatra-billion-gazillion?
Yeh, me too.
But sometimes it's easier said than done. One of the best tips I've ever heard on how to show, rather than tell, was to imagine your scene as if it's on a movie screen, then describe in detail what is happening.
For example, let's say we have a budding high school romance. Boy and girl are discussing their feelings for each other. Instead of telling us that he is embarrassed by the things he wants to say, or that she is afraid he's going to dump her, picture the conversation on a larger-than-life, techni-color screen in your mind. What does it look like? Show us through your description.
Does the boy shift his weight from foot to foot and look off into the distance? Does he open his mouth to say something, then close it again? Do his ears turn a little pink at the top?
And what about her? Does she hold her books up close to her chest, as if they'd protect her from the blow of his words? Do her eyes water up just a bit and does she bite her lower lip? Does she look down at the ground, then back up at him?
The description and the choice of their dialogue (or lack of it), show us that he is embarrassed and that she is afraid. That's what we mean when we say show, don't tell.