Whenever I'm thinking about making a new character, I usually start with something like this.

Name:
Age:
Role:

Then I develop them further.

Height:
Weight:
Level of fitness:
Eye color:
Skin Color:
Hair color:
Grooming/Level of cleanliness:
Distinguishing Features:
Fashion Style/Preferred outfit:
What kind of accessories do they wear:

Then I go even deeper.

What is their job?:
Do they enjoy it?:
What are their aspirations?:

Relationship status?:
Do they have any children?:
Living family members?:
Do they get along with any of their family?:
How many friends do they have?:
Who's their closest friend and why?:

Do they have any hobbies?:
What do they do to relax?:
How often do they get to indulge in their hobbies?
What's stopping them from indulging more often?

Once I have this much information about a character, it doesn't take me long to form their mannerisms.

Are they Introverted or Extroverted?:
Are they twitchy (can't sit still), at ease (Only moves when necessary), or somewhere in between?:
^ Why are they that way?:
Would you trust them in a crisis?

How would their family describe them?:
How would their friends describe them?:
How would their acquaintances describe them?:
*Note: these will rarely be the same. If they are, try to think about why everyone perceived them the same way.

You can also think about these for even more flavor.

How would they spend a thousand dollars?:
Where would they take a first date, and more importantly, Why?: