What are the rules of proper managing the credit?

One rule you shouldn't break in credit management: Never go past two due dates without paying a fraction of what you owe or what someone owes to you. Letting the credit amount (yours or someone else's) reach its due is reasonable once or twice when you're struggling to find the means to pay the interest each month. This problem is especially common among business owners who borrowed a loan to put up their companies. If you want, you may seek the assistance of a credit consultancy firm. They'll know what to do, and they're more familiar with the credit laws in your country.