Your already 1/2 way there. Your thinking bigger picture which means your able to weigh risk versus reward more accurately.
Having joined a 5 man company right out of college and growing (500%) with it for a decade and then seeing the tech bubble bursting take it down matured my perspective.
Study the sandbox:
I'd highly recommend getting intimate with the market that the company serves and the competition in that market. You want to make a determination on where you think the market will be 5 years from now. As the market goes the company goes. You also want to take into account how the startup in financed.
Study the ship's captains:
You will want to get as good a feel as possible for the owners of the company. If you sense a clash of personalities it is sure to be a bad long term sign. The reverse is also a good sign.