It's worth remembering that it's not uncommon for 200 people to apply for one position these days. It stands to reason that almost everyone will have a poor success rate, and becoming demoralised about it will further affect your performance. I've interviewed people in the past and there'll often be 15 people all exceeding the requirements, and we've had to pick the best based on little more than a guess.
Have you asked for feedback from interviewers? Obviously if your answers are poor, then it's worth a wholesale change in how you answer the questions (e.g. if you don't use something like the STAR method mentioned above), but it's easy to become demoralised by assuming your answers are bad (and sometimes change a good answer) when you're simply being unlucky that another applicant has 10 years more experience.
I think the main thing to take into an interview is confidence in what you're saying, and self-belief. Sounds both obvious and easier said than done, but as long as you believe that the examples you give, and reasons why you dealt with certain situations in a certain manner do show competence, you'll come across a lot better than if you're not sure whether your answer is 'good enough'. Why are you good at your current job? Build your answers around that (try not to over-prepare, but the obvious questions can be prepared-for in advance).