Complete a fresh mix of customer and vendor work. The ledger effect is only part of a useful record: the correct contact, bank account and source form keep customer balances, vendor balances and bank reconciliation aligned. A customer payment entered for the wrong customer can post the right total while leaving the actual invoice open.
Read the destination on every money movement. A deposit to Savings is different from a deposit to Checking, even when both are assets. Use credit memos for unpaid sales allowances, vendor credits for returns to suppliers and Pay Bills for existing obligations. Keep a partial amount open instead of marking an entire bill or invoice settled without evidence.