Just because you failed the job interview doesn’t mean that you need to focus only on the negatives. The first thing you should do is figure out all of the things you did right. Those are the things you’ll want to build up in the future, and figuring out where you succeeded will help you be a strong candidate in the future.
Try to write out as many questions as you remember. Don’t worry about the answers yet. Just write out every question you can think of on a piece of paper so that you have it as a reference.
Mock interviews are an important part of practicing. They involve holding a fake interview with a friend so that you’re comfortable with the process. In this case, hold the SAME interview that you just went through. Have your friend ask you the same questions, and try to come up with responses on the fly.
Only after you’ve held a mock interview a few times, try to come up with the best answers possible. Chances are you’ll see many of those questions again, and if you do, you will want to be able to answer them confidently. Use your mock interview and interviewer as a reference to see if any of those answers were strong.
Finally, if you know you didn’t get a job, call the job interviewer you had and see if they can give you any tips. Yes, it can be a bit nerve-racking to hear what you did wrong from someone, but the only person that knows every problem you had is the person that interviewed you. Call them up, find out what you can, and use that information for future interviews.