A clear scope.
A useful brief.

Define the ongoing work, clean-up volume and systems involved.

Establish the filing type, corporate structure and readiness of the year-end file. Canadian T2 / GIFI terminology applies to Canadian corporations only.

Scope pay processing, year-end work and payroll account support separately.

Identify the tax account, filing cycle and transaction mix. GST/HST is Canadian; other GST, VAT and sales-tax work needs jurisdiction-specific confirmation.

Define the reporting output and intended use. An audit or review engagement is not automatically included.

Separate incorporation administration, corporate records and accounting setup. Legal advice and government fees are confirmed separately.

Identify a concrete decision, expected output and available records.

Tell us what is in the return, not just that you need one. Canadian terms below apply only to Canadian filings; identify other jurisdictions in your context.