Every landlord has their own criteria for which tenants they approve to lease office space in their building. At the end of the day they just want to make sure you have the ability to pay rent and have a solid business plan that will generate income. Below are a few things they will want to review before allowing you to lease office space in their building.
1. The last 2-3 years of tax returns. If you are a startup they will want to see your personal tax returns
2. Profit / loss and balance sheets statements (if you have them) that show you have enough cash flow to pay rent. If you are a startup then your personal tax returns and a personal financial statement.
3. A detailed business plan describing your business, it's objectives, financial goals, etc. The landlord wants to see that you know your business and have a solid plan to ensure its success.
4. Sometimes landlords will require you to sign a personal guarantee if they don't think your business financials are strong enough on their own. If you default on the lease then the landlord will be able to come to you for rent payments. If you agree to this make sure to put limits on it (e.g. only personally guarantee the unamortized tenant improvement costs, commission, etc…)
5. A resume or professional references will sometimes be asked for.