Write down the questions you were asked, your answers, and what the interviewer said. Such information can be valuable in preparing for future interviews. Also, because you may have more than one interview with the same person or with the same company, you can be consistent in what you say. If you are qualified for the job, have prepared yourself well, and put your best foot forward during the interview, you stand a good chance of succeeding. The most common reason companies give for choosing one applicant over another is personality and overall impression of the candidate.
Grades are surprisingly low on the list.
Companies say they want top graduates, but they really want amiable, well-rounded workers who are highly motivated, can communicate well, and have the skills that the company needs. Do not be discouraged if you do not get the first job for which you apply. Review each interview and decide what you did to make a good impression and what you might do better. Then try again.