How to approach potential advisors? (who are famous)

It's tough if you don't have a special angle to communicate, because by definition it sounds like they'll get a ton of email about startups.

A way to break in is use Twitter and @name them for a few weeks about stuff they honestly would be interested in. That way at least they've heard of you at all -- even very famous people still read those @tweets.

Next your email needs to scream that you're unique, smart, and have a solid idea. That means you cannot say "Unique exciting startup idea!" (That's what they all say.)

Instead focus on those rare but actually-exciting things like:

• customers
• revenue
• how much you've accomplished with no money
• how little money/advice you need to move forward (just the right advice)
• be very specific about what type of advice you need and why that would be transformative

So for example a single-line customer testimonial is more interesting than you talking about features. Saying you got 10 customers just by cold-calling is far more interesting than a sales strategy.

Typically this is made via introductions/recommendations; If you don't have any, it's tough.

I suggest you proceed and send them a short and straightforward e-mail, stating for example what you've mentioned here. "You have already greatly impacted my startup and gave me tons of solid ideas on how to reduce research costs to almost nothing" is a great punch line nobody wants to skip. Try not to sound like begging though, being extremely modest or shy makes your request boring and lowers your chances to get a reply; plus they used to be just like you or worse, no reason to feel so.