When you first create your main character, there is a lot you will need to consider...
The physical traits
You will need to redraw tons of times your main character. The hair, the eyes, the posture... I can't remember how many times I had to redraw Alexandrina, the Queen of my manga METIS.
Make sure all elements you are perfecting for your character will match her personality, unless you want to create a strong contrast.
The characters here have their own particular traits. The one of the very right side - her name is Laoïs. I first created her late 90s, and she kept on changing! See below...
The keys to finding the physique of your character
Never hesitate to play around until you find what you were looking for.
All great mangakas never stick with their very first idea;
most editors will ask them to change.
When I first created Alexandrina, her name was Hillary. She was to be 14 or 15 years-old, cheeky and smart. She had a very round face and big eyes.
I then decided to make her look older; her chin got pointier and her face less round. Her eyes were still black but their shapes were narrower. The nose was sharp and she looked like she was at least 25 years-old. I wasn't too happy about that characterization, but it was the one I kept the longest.
It took me about 5 years to find the final character design: a mix of childlike features and impersonation and intelligence of a grown-up.
When you read manga, you can clearly see the evolution of the characters. A mangaka always improves and develops her skills. And practising is the key.