"Carefully managing debt" can be summed up as one single principle: be aware of deadlines.
It's ok to use a credit card as long as you know the deadline to pay it in full and you do so diligently in order to avoid insane interest rates. If you can pull this off, you can actually earn money with credit and debt (e.g. rolling credit card over new credit card with 0% interest, over and over). Just make sure you don't miss any of the deadlines.
Same goes for my little anecdote above: it works great if you're aware of simple deadlines (how long I needed these $30k to be in the account) and elementary level math to compare 1.5% and 3%.
I used to think everyone should be able to handle this simple math approach but if the US population is any indication, I am dead wrong.
Debt is good. Don't be afraid of it: tame it and you'll start earning easy money.