How do you approach technical due diligence?

Hey HN Brains Trust,

I've been asked to perform a technical due diligence exercise on a company that mine is considering acquiring.

I'd love to learn from those who have tackled a task like this before. What did you learn that you wish you knew ahead of time? What do you wish you had asked? Do you have any general advice or guidance you think someone in my position would benefit from knowing?

Cheers,

Derek