I spent 5 years at McKinsey before startups and I often get asked for advice by consultants considering startups. here's what i say:

(this is more for seed/series a/founding):

And there’s no substitute for practical experience.

Many people in “steady and sure” career paths would be better served being less risk averse and just taking the leap.

The skills you gained in talking to customers will serve you but also much of what you've been trained to do is worthless at a startup

You need to unlearn the following:
- Powerpoint slides as the work product
- Process for its own sake
- Caring about office politics

But you should keep the following:
- Customer/Client obsession
- "Walking the halls"
- Project management (useful for B2B sales)