This entire thread is gold. This is a direct rip off from the top most comment. Saving it here because, well I might need this sometime.
I can’t boil it down to 3 because there are many things you need to understand, some details can be gleaned via observation too.
So some of the top questions you should ask IMO are below:
When was the last raise, what was the amount and time to raise it? What is the makeup of the investors (Angel vs. VC etc)?
What is the next milestone on the fundraising side?
What is the biggest competitive advantage/product feature the company has?
What are the biggest issues facing product/development?
How do you see my role helping the company?
How can I best help the company if I come aboard?
What is the biggest opportunity you feel the company has?
What is the biggest risk the company faces?
Who do I report to? – this trips some startups up, but can highlight potential issues.
How many employees are there today? How many do you plan to hire in the next 3, 6, 12 months? How many employees have left since founding?
Equity and the vesting schedule details. Share class information as well. Current dilution, outstanding shares issued and reserved is nice to know too as well.
For what it is worth and this applies to any size company not just startups, you should also ask about what agreements they want you to sign and get them as early into the process as possible without being unreasonable. e.g. outside work policy, NDA, non-compete, non-solicitation, compensation, equity etc. Some of these they may not give you until you agree at least conditionally verbally, but there should be no reason you can’t see them once you do. Companies that hide these until your first day make me nervous, at the same time that doesn’t mean they are bad, just maybe been given bad advice or have a lack of understanding themselves.