Oftentimes, a prospective new employee for a start-up is offered stock options as a significant part of their sign-on bonus, if not the entire bonus.
When given an offer, say, of an option for 20,000 shares, what information should the prospective new employee gather, either by asking the company or through research, in order to correctly evaluate the value of the stock options?
Assume for the purposes of this question that the start-up is not known to be imminently pre-IPO, and it's not as simple as searching for a stock valuation - this would be for a start-up in the "quiet" period where the only publicly disclosed information is the funding rounds and amounts, either no revenue or no disclosed revenue.
If it matters, I'm specifically interested in the biotech sector, but would be happy with a more general answer if the information needed tends to be similar across industries.