The purpose of cash flow from operating activities statement is to find out net cash flow resulting from routine operation of business. Under indirect method, Net profit for the year should be adjusted with non cash transactions which affect Net profit for the period to find out actual cash flow. For example, if the reported Net profit is Rs. 1,000, many non cash expenses eg. Depreciation results in reduction of Net profit. So we cannot say that Rs. 1,000 is what company has in hand from operating activities. So if the depreciation is Rs 50, actual cash company would have Rs 1,050. Like that all non cash expenses should be deducted and non cash gains should be deducted (vice versa) to find out actual cash flow from operating activities.
Basically logic behind treatment of all items you have mentioned is same. Below are some explanations:
General Reserve: Debit balance would be transferred to P&L and results in reduction of net profit but not operation cash out flow for company. So should be added to Net profit.
Provision for tax: Ditto
Proposed Dividend: Payment of Dividend is not an operating activity but including the balance in P&L results in reduction of N/profit. so should be added to Net profit to arrive at cash flow from operating activities.
Preliminary Expenses: Usually will be debited to P&L account in the period in which incurred, thereby results in reduction of net profit. As it is not an operating expense for the period and should add to net profit in cash flow statement.
Depreciation: is a non cash expense, which when debited to P&L account, results in reduction of net profit. Same treatment as above
Loss on sale of FA: Are non cash expense, when debited to P&L results in reduction of Net profit. Treatment should be same as above.