Timeliness first
Monthly accounts produced within two or three weeks of month end signal control. Figures that only exist once a year, at the accountant's office, signal the opposite.
You do not need sophistication. You need consistency.
The breakdowns that matter
Revenue by customer and by service line. Gross margin by the same. Recurring versus one-off income. A debtor ageing report. Headcount and payroll cost. Pipeline or order book.
If a buyer can see where the profit comes from, they can price it. If they cannot, they discount it.
Reconciliation
Your management accounts should land somewhere close to your filed accounts, and any differences should be explainable in a sentence.
Unexplained gaps are the fastest route to a longer, more expensive diligence process.