it's mostly a matter of having information that the market doesn't, which normal people like you and me prob don't have access to

that doesn't mean that nobody does well - by definition, half the people will do better than the median over a given time period. but for most of them, it's not likely to be a performance they can repeat

the advice about index funds is standard now, but what you really want to evaluate is your mentality and think about whether you can psychologically stomach being invested 100% in the the total stock index or if you need something a little more conservative/balanced. people think they can handle the volatility, but when you randomly see or hear that the dow jones dropped XX% today, will your first instinct be to sell? and will you be able to override that instinct?