Secondly, if you need to, don’t do it like this:
EXAMPLE: “Sarah had blonde hair, green eyes and a straight, white smile.”
Why? It’s boring.
Yes, people have eyes, yes, they have hair. The reader can conjure this up for themselves. But what you’re doing is merely describing her features, instead of what you should be doing, which is creating an impression of her. That’s what the reader can’t conjure up for themselves, because at this stage they don’t know your character.
So, ask yourself: How does Sarah’s personality affect her features? She might be a complete bitch?
She could have a stubborn pout.
She could have a wicked glimmer in her eye.
She could walk from her hips, as if she owned the whole world and everyone in it.
Her smile could cut like a razor.
Her skin could be like cream.
This way you create an impression of your character and paint a deeper picture of who they are as a person.
Don’t get stuck on looks. Create an impression.