Begin with the everyday.
Ask about access, deliveries, storage, outdoor space and building services. Confirm features for the particular apartment rather than assuming they apply throughout the building.
Understand the rules that matter to you.
Ask for the current building policies relevant to your plans. Renovations, pets, occupancy and leasing can involve different requirements; verify the actual documents.
Make room for professional review.
Ask your attorney and other qualified advisers to review the documents, obligations and risks relevant to the property. A listing description is a starting point, not a substitute for due diligence.
Keep a written question list.
Unanswered questions are easier to resolve when they are specific. Record what needs verification and who will provide the answer.