If you do it as a hobby, count on losing every penny you put in, and treating that as the cost of pursuing your hobby.
If you do it as a business, count on working on it full time, i.e. AT LEAST 40 hours a week, and probably more like 60-80. The competition is fierce. And I would not do it with less than $1M in LIQUID assets which I could afford to lose. The reason you need this much is that in order to have a good shot at a return you need to be able to do two things: 1) invest in a pretty broad portfolio (i.e. at least 10 companies) and 2) have enough money to participate in follow-on rounds so you don't get diluted into oblivion.