Debtors, stock and prepaid expenses are operating assets used in the profit making process. Creditors and accrued expenses payable are operating liabilities used in the profit making process.
Operating asset increases and operating liability decreases are negative adjustments (decrease cash flow from operating activities)
Operating asset decreases and operating liability increases are positive adjustments (increase cash flow from operating activities)
Depreciation and amortisation expenses are positive adjustments (increase cash flow from operating activities)
Cardinal Rule: Make all cash flow adjustments to net income; don’t simply add back depreciation and amortisation, which could be seriously misleading to your auditors.