The Purchase Ledger
The most useful management report is the Aged Creditors - this shows the ageing of all your purchase ledger accounts. You should feel comfortable that this is in good order otherwise you may pay suppliers the wrong amounts and your management accounts will be incorrect. Any negatives need a good explanation. This could indicate a missing invoice, in any event these should be checked carefully. Wherever possible these balances should be reconciled or agreed with statements from your suppliers. Most businesses miss doing this and therefore risk errors. Not all suppliers produce statements, so ask for one, either occasionally or monthly. You can always say that you will only pay on receipt of such. It's a really good way of picking up overpayments, such as paying an invoice twice or not picking up a credit note when you make payment. For reconciling the purchase ledger see below re sales ledger.
The Sales Ledger
The most useful management report is the Aged Debtors - this shows the ageing of all your sales ledger accounts. You can print in summary or in detail showing every outstanding transaction. It's sensible to review this monthly, especially the older columns and take action as required in chasing the debt. Reconciling the sales ledger means checking that the total on the Aged Debtors report equals the balance in the Nominal Ledger i.e. your accounts. In case there are future dated transactions, use a reporting date that is forward so that everything is included. In theory this is self checking as a posting to the sales ledger must update the Nominal Ledger however it's possible that a journal has been input directly to the Nominal Ledger, upsetting the agreement. If so then this posting must be reversed and this transaction handled directly through the sales ledger.