I developed my best insights into credit scores around 2001 or so: that's it's less a measure of how responsible you are, and more a measure of how good a banking customer you are.
I'd been living a number of years pretty much "cash basis". I had no payments of any kind - no car payments, no mortgage, no credit cards. I didn't even use credit cards; I had a debit card on the VISA network, and an Amex Platinum (the fancier card is good for international travel). I decided to rent an apartment in Buckhead just as a crash pad, since I was living in Cartersville at the time and sometimes it was inconvenient if I had meetings in Atlanta over a few days.
The apartment wanted a deposit. It kind of floored me, because I made a good income, had cash in the bank and healthy investments, and was Mister No Debt Ever (I made sure college was free, and had kept up the never-finance practice). It turned out that wasn't as good from a "credit score" perspective as having and keeping revolving obligations.
Once you understand that, credit score pumping becomes a matter of gaming the system... making sure you have loans, but hacking things a bit to minimize the bite of interest (for example, I do have a mortgage on a property currently, but I pay two extra months a year, which greatly reduces repayment time). I still use an Amex for pretty much everything (I can rack up 200k+ points per year, which I hoard like Smaug), and use a Visa for those quirky times Amex isn't accepted (paid in full monthly).
I monitor credit also; I HAVE found errors on mine (because of a relative with the same name), and I challenge them per whatever tools the reporting agencies offer.
DH