When I thought I might go after a mortgage on a new house 3 years ago was the last time I checked. My 3 credit report scores then were all over 900 - I think it was 925, 940, and something similar. Haven't checked again since then, though I guess it's time to check again! But, here's what I do:
I have and use only ONE credit card, and I charge all the time to keep my credit active. I use it for buying everything, even groceries! Then I pay off the whole amount when I receive the bill each month. Am racking up lots of nice points to use on Amazon that way, too!
I paid the mortgage on my first house by paying double each month, sometimes even triple. Sold the house at a profit.
I only have one negative thing on my reports - a single late pay to a utility from several years ago. Just pay your bills in full and on time. How hard is that?
I fought one attack from a company - Swiss Colony - which for some reason never received a check I sent them in payment
for a bill. Who knows what happened to that check. Anyway, in a phone conversation they said they'd give me a month to send another check, but then they started charging me mega interest and sending threatening letters almost immediately. I went straight to the Better Business Bureau on-line and filed a complaint. Swiss Colony backed down right away. Don't buy from that company! IMHO they make most of their money from charging interest on credit they extend rather than on the actual products they sell. I think that's true about a lot of catalog companies.
And finally, if I don't have enough money in the bank to pay for something, I don't buy it.
Before you start thinking I'm too irritating, here's my truth: I DID get in credit card debt back in the late 1980s when I was in grad school. My parents ended up lending me money to completely pay off the credit card company (about $4000 or so) and then I had to pay my parents back a monthly amount to pay their loan off. Got a job, lived frugally, and paid them off in just under two years. Learned my lesson.