Here at Job Fairy, we call this "finding your center". You have to look at yourself, realize what it is about you that makes you unique, and know that no one else can offer this. Any employer would be lucky to have you. You're doing them the favor - it's not the other way around. You don't call recruiters again and again, hoping you were the one picked for the interview (or the second, or the third). You don't call employers repeatedly after the interview either. In fact, you don't call them at all. If they want you, they'll move heaven and earth to find you.
You're not insecure. You know you're the best candidate; you have great self-esteem. If the company doesn't pick you, then it's their loss. If you do The Rules, often you won't get picked for a particular position. That's OK. The job probably would have been too stressful and it might even have wreaked havoc with your personal life. The Rules are intended to raise the cost (see De Becker). This way, toxic managers get a sense right away that you might not be pliant or needy enough to put up with their bad behavior. They have to come to you; you don't have to chase them - you're aware of your intrinsic worth.
You don't reveal too much in the interview. You answer the questions, and not any more. If the interviewer is silent - you wait. You don't start blathering in an effort to cover the silence. You let them do all the work. Don't be awkward and jerky when you move around. If necessary, take a dose of cough syrup before you leave for the interview (the non-drowsy kind). You won't hack, sneeze, or rub your nose - and you will probably be more relaxed. You fold your hands into your lap so you don't twirl your hair, bite your nails, or tap your fingers nervously. You sit up straight in your chair, but not rigid. You're at ease. It helps to do daily affirmations at first, until you know that you deserve the best that life has to offer.
No matter what else is going on in your life, you don't reveal it. If your spouse just walked out on you the day before, it doesn't show. You're dressed appropriately, you're well-groomed, and you're composed. The Rules says that even if this isn't the way you really feel, you make yourself feel this way until you really do eventually feel this way. You're re-training your reactions to certain situations in this fashion. It's like giving speeches in public. You may be nervous and shaking on the inside - but people can't actually tell. Make sure you breathe deeply; don't make the mistake of speaking rapidly out of nervousness. If you slow down your words, making them come out in a more deliberate manner, you won't speak with a nervous tremor in your voice.
The only difference here from the classic Rules is that you always bring a copy (that's one) of your resume to the interview with you. It's supposed to be for your reference. Sometimes the hiring manager doesn't have a copy of your resume with them, and needs to look at yours. That's a signal that they're interviewing so many people for the position that they didn't even have time to prepare or weren't organized enough to prepare for the interview properly. Take note of this; if they're like this in the beginning, they will be like this throughout your employment there.