Describe with action, dialogue tags, or dialogue what your characters are wearing. You don't need a paragraph about what they are wearing, unless fashion is extremely important to the plot. You can work descriptions in easily. For example: Before Beth could tell Sam she loved having dinner with him, the waiter tripped and spilled red wine down her blue, silk blouse. (Instead of writing: Beth wore a blue, silk blouse on her date.)
Write about a couple physical traits. You don't need to describe every single body part--this is not a dating profile. Here's an example that will give readers a picture about Beth: Beth pulled her curly, blonde hair into a ponytail to show off her small ears, highlighted with diamond stud earrings. (Or a different picture: Beth ran her fingers through her spiked hair before putting in her nose ring.)
Currently, I am writing a young adult novel about a 17-year-old girl named Julie. Julie is a nervous teenager, but I don't come out and tell the reader. I show her nervousness with my description of her actions. She has sweaty armpits, twists her hair, and has a jumpy stomach. Is your character energetic? What traits can you give him to show this? Think about ways to describe what your character is like without telling the reader.
I also use dialogue to describe Julie in my novel. You can do this easily. Is your character from a certain part of the United States or world? Think about the vocabulary your character uses or the way he or she talks. Julie is a nervous teenager, so she talks really fast with long, run-on sentences full of adjectives.
Your character has hobbies, family, and friends. Use these to describe your character, too. In my novel, Julie loves Katharine Hepburn because her mom, who is deceased, had a collection of Hepburn items. This shows Julie is unique and also misses her mom. I don't come out and say this in my description. I show it with her hobbies and conversations with family members and friends.