Something a lot of authors seem to forget is that body language plays a big part in our communication. In fact, research has pointed out that body language makes up for 55% of our communication. Another 38% of communication is conveyed in the tone of voice, and the words we use is only good for 7%. And though you might say that, as an author, you work with words more than anything else, it is important not to forget body language and tone of voice in your dialogues. It will give your writing colour and it will help to create an atmosphere.
Also, think of giving your characters their own little quirks and ticks that come out through their body language. This will make your characters more relatable and it will help you to deepen your characters out: make them 3D personas.
There are some helpful books on the market that can help you to add some flavour to your characters. One of them is the Definitive Book of Body Language, which has helped thousands of writers to describe their character’s feelings, dreams and wished through nothing more than body language.
Another one I like to use is Unmasking the Face. This book is completely focussed on the face as it not only helps you to read people’s faces, but also describe the emotions playing on the face of your characters.
Now these sources should be able to help you further in your writing endeavours, but I would like to warn you not to overuse common forms of body language as it can negatively impact the pace of your book. Instead, try to describe these actions with different and unique words and sentences to keep your reader surprised and hooked.