Here's what 20 years of experience working for startups has taught me:
-- Either be a founder if you want to be there in the early days.
-- Or join a "sure thing". EG: Google, Twitter, Facebook about a couple years before they went public were already household names and really well known.
I don't know how much upside you get joining a sure thing like that, but that's how you make sure your options will come into money.
Being employee number 5-100 of the average Silicon Valley startups is a losing proposition because the risk adjusted value of your options will never compensate you for your lost salary. (especially if you have to live in California- you're better off working for a startup in Austin than California due to the cost of living and tax situation. The higher salaries in California don't cover the difference.)
And yes, blame me, I turned down being employee number 13 at what became a $6B enterprise software company. Would have been CTO or way up in the executive team because they were a bunch of biz guys who needed a hacker. Instead I worked for just a year for a small business (not really a startup this was before "startups")
But it's damn hard to tell the difference at those early stages.
And when questions like "what's the total number of shares outstanding on a fully diluted basis?" (back when companies would say "You'll get 10,000 shares!!!!111!!") are met with "sorry that's confidential" during the hiring process, it is a bit difficult to do proper due diligence.