Stocks are the best passive investment: they don't require you to actually do anything, unlike a business or real estate, etc.
I recommend that most new investors get what is called an index fund, such as an S&P fund. These funds have very low costs (usually about .1% or so) and outperform almost every other fund over the long haul.
Basically, rather than buying and selling stocks all the time, the mutual fund manager just buys and holds the stocks of the 500 largest companies on the exchange. So you are diversified (you have lots of stocks) and you don't rack up a bunch of fees buying and selling stocks. These funds average about 12% return historically.
There are ways to get better returns. One way is value investing, which I do, which relies on buying companies that are "cheap" relative to the rest of the market. Perhaps their price compared to their innate book value is very low. This strategy tends to outperform the market; over 4 years I have beaten the index by right around 10%. Personally, I look most at price/sales, then price/book, price/earnings and dividend yield.
Others do technical investments. Personally, I don't understand what they do, but craazyman and systems trader are both outperforming the market in the long term, so I recommend talking to them.
http://en.wikipedia.org/wiki/Value_investing