Actually, FICO scoring doesn't give a hoot about your debt-to-income ratio. Mortgage lenders certainly will, especially now that ninja loans are no longer on the table. But FICO doesn't.
To make a long story very short, FICO scoring cares about:
* You paying bills on time
* You having at least three or four revolving accounts (i.e., credit cards), and preferably an installment loan and mortgage too
* That you keep your revolving balances low relative to credit limit.
* That you have had credit for at least three years or so.
That's about 80% of your FICO score, in a nutshell.