The 3 golden rules of bok-keeping are:
Dr. Expenses Cr. Income e.g. Dr. Rent Cr. Sales
Dr. Receivers Cr. Givers e.g. Dr. Debtors Cr. Creditors
Dr. Assets Cr. Liabilities e.g. Dr. Cash at Bank Cr. Accounts Payables
Overall, the basic formula of a financial statments is
Assets - Liabilites = Retained Profits ( Income - Expenses ) + Share Capital