Lots of commands do a financial workshop that can explain things like credit to debt ratio
Something I was going to bring up. You could have ten million dollars in assets, but they don't care. Having a crap ton of money doesn't make you credit worthy. Credit worthiness is a function of your ability to manage your credit, so the company knows that if they extend you credit (loan you money), you're not going to take every penny you can get it and run. The easiest way to judge this is based on your debt/credit ratio. Simply put, the higher your available credit is and the less of that credit you're actually using, the more credit worthy you are.
This is a primary reason they say not to close your oldest accounts. Even if you don't use them, they likely have your highest limits, and therefore improve your ratio.
5 months ago when I went to get a new car, I applied for the financing through a bank with one credit card and some student loans in my name. I got an interest rate of %XX. I then opened a new credit card with a completely unrelated bank a week later it had a $11,000 limit on it. The week after that, I went back to the bank I wanted to finance with and requested a new loan for the same terms, and my interest rate dropped nearly %6... down into the single digits. all because I had improved my ratio.
now personally, I went and closed that new credit card because it had served its intended purpose for me, and that was the best $50 I ever spent going through the hassle of closing a brand new card like that just in the interest it saved me on the car financing. I wouldn't recommend doing it this way though. It was underhanded, and oculd easily backfire on you. Just don't do it.