There is a few ways of looking at this.
1. Debt / Assets. Take your debt and divide it by the MARKET VALUE of your assets. Don't over complicate it. Debt should be all short and long term debt. Assets could be cars, home, retirement saving, savings etc. Logically, if the ratio is above 1, you should be worried, because your debt outweigh your assets. So, if you don't get an income. Mine is currently 0.17 : 1. Meaning, for every R1 asset, I have 17c debt.
2. Total debt / Gross income per annum. I use this, but it might not be of value to most people. It is a quick indicator on how far down the line you are with your debt. Remember that the gross income include salaries, rental etc. Mine is really low, due to only a home loan being paid off. 0,51 : 1.
3. Total payments to debt / Net income (can be monthly or yearly). If I recall correctly, the average South African is about 76%. So, how much to you pay back on home loan, car loan, clothing accounts, cellphone etc. compared to your net salary. Mine currently is 15%.
Note, that my nickname in my family is Scrooge or the Jew. (no, I'm not Jewish). I'm quite conservative with debt and debt accumulation.
EDIT: Last note. I had a conversation with someone yesterday. We sacrifice long term savings for retirement for instant gratification like gadgets, clothes (and cars). Most of us will pay off our debt, but in 20-30 years time when we retire, the retirement amount will be too small, because the money spend on luxuries could have gone to savings for the future.