Start with a real question
Can you explain what a payment was for and find the document behind it? Start with the date, counterparty, amount, currency and purpose. Keep the original receipt or invoice beside the entry. A bank statement shows money moving; it may not explain the business reason.
Separate evidence and summary
Use a consistent filename with the date, supplier and invoice reference. Link the file from your summary. Preserve the original when you make a translation. A screenshot of a total is not the complete invoice. Mark missing documents as missing and ask for them instead of inventing a category.
Keep founder movements clear
Do not silently label every payment from a founder as revenue or every payment to a founder as an expense. Record what happened and ask the accountant about the treatment for this entity. If personal money paid a business cost, preserve the cost document and reimbursement trail.
Review exceptions each week
Review missing invoices, unexplained transfers, duplicates and mixed currencies. Keep the original currency amount alongside any conversion and its source. Give unresolved items an owner and next step. A tidy folder is not enough if the numbers cannot be traced back to evidence.
Ask before deleting
The IRS says a business may choose a system that clearly shows income and expenses and should retain records as long as needed to support relevant tax entries. This is US federal guidance, not a universal deadline. Ask a qualified adviser about your jurisdiction and document types. This checklist is not tax advice. Source: https://www.irs.gov/businesses/small-businesses-self-employed/recordkeeping