What is the most important thing to care about in an interview

To be trust in your potentials, capabilities, abilities, and tools.

To respect the interviewer and to attend in time and in a professional suite

To stay calm.
Don't be nervous.
There are various things you can do, prayers to recite, breathing exercise you can do to keep calm.
The time before the interview is very important.
Get to the company early so you can relax for a little while.
While you may use the time to rehearse some things you might say in your mind, but don't overlook the importance of relaxing.
Read some prayers that will help take your mind off the interview and ask God to help you say and do what is right.
That way, when you enter the interview room, your attitude will have a good first impression and you'll be better able to answer questions and talk about your qualifications and skills.
Finally, always be truthful in an interview.
Never lie.
Even if you must say you have no experience, go right ahead and do so instead of lying.
Be sure to talk about any skills you attained through volunteer work, course /academic projects, community service, or even at home doing chores for your family.
Maybe babysitting your siblings gave you patience and quick-thinking skills that the interviewer might find just right for the work environment.

it depends on the position you are applying for, in general one must focus on :
1- professional image
2- experience
3- skills that are relevant to position
4- what will make you the perfect candidate for the vacancy
5- what makes selecting you an added value for the company
6- your general view for planning, decision making and improving work environment