The most important thing is being educated. Every time this topic comes up on HN it appears that many people are unaware that liquidation preferences are a thing and many sales that are down-rounds have no money falling on common.
If you are paid in stock, and the founders make a deal that reduces the payout value of that stock (in this case to zero) they have stolen from you in a way that has no recourse. Literally they paid you with something that was presumably claimed to have value, and then after a few years made deals that made that worth less. Even though you had already been “paid”.
How much education can you do that would protect you from this?
Given how much the big tech companies are paying though, especially when it comes to RSUs, I'm not sure this calculus makes sense anymore, especially for early employees. Founders may do exceptionally well on many cases, but for most early employees at startups there really isn't that much potential upside in most cases, compared to the guaranteed earnings you can get at a top tech company.
I can confirm that RSU payouts at the giants far dwarf what you can get at almost all startups. The total comp difference is insane.