Starting a story, you should have your characters planned out. Not just their name and their age. What I usually do is think of a backstory to go along with them. How was their childhood? What had happened recently to lead up to now?
I then think about their looks. Is their hair short, long, always up, always down, curly, straight, what colour is it, do they dye it, etc. What colour are their eyes, do they have long lashes, what's their eye shape, do they wear makeup?
Then I move on to what kind of style their clothes are. Causal, preppy, dark clothes, colourful, always a suit, always a dress, etc. Not that I am going to describe their outfit every time they change, but just so you can visualize them from head to toe.
After I have all of the physical attributes down, I think about how they speak. Do they use long words, do they always sound happy, do they contract their words, etc.
After you have all that, and you begin to write, do not start off with blatantly describing them. For example:
Hi, I'm Beth, my hair is brown, short and curly and I am chubby and short. My nose is small, and my eyes are green. I'm about 5"1 and I'm super insecure.
Or anything like that. Try to keep the character's look a mystery, describe them slowly throughout the book.
He runs his fingers through his dark hair
He looks at me with his piercing green eyes
His frame cascades over me like a tower
His thin arms wrap around me.
Just some ideas to pop into your story at random to describe the character without blatantly describing them in the first paragraph.
