Ask HN: What do you wish you knew about scaling when your start up was small?

I'm writing a book for founders and early stage engineers who want to know how to set up a website/app correctly so it can scale later on.

What are some things you wish you knew before your start up took off? Could be tools to use, best practices or even things you wish you hadn't done. I'm hoping to keep things light enough that even a technical but non-engineer founder would benefit from reading it.

If you'd like an update when the book is ready you can sign up here: www.startopsbook.com