It is wise to apply for more than one vacancy at a time, so you always have more interviews ahead of you. This helps to keep a sense of perspective about the process and keeps you from feeling demoralised if you don't get a job. It is easy to become depressed about lack of success in job interviews. However, the most expect interviewees may be turned down just because, on the day, there happened to be somebody who seemed more suitable. If you are rejected, it is worth contacting the employer to ask for some feedback on your performance in the interview.
Most employers are keen to help as long as the request is phrased politely.
Another antidote to feeling despondent about searching for work is to mix with other people in the same situation. A supportive group can keep you going when you feel at the end of your tether. At times you will need to fight the feeling that there is something wrong with you as a person. Sharing your experience with other people will remind you that there are other excellent candidates who fail to get jobs. Maintaining some semblance of a work routine is also helpful in keeping up morale.