Index funds are usually a good idea in the long term, but right now (June 2017), I would not put a penny in the stock market - it is ridiculously overpriced.
Stock markets in the developed world have risen too much, Robert Shiller, economics professor at Yale, told CNBC Thursday.
On Wednesday, the Dow bounced above and below the psychologically-important 12,000 for much of the session. But stocks look expensive, Shiller said.
"I would say the market is overpriced based on fundamentals … I'm talking about the US and probably Europe," he said.
[The market has almost doubled since then.]
Thus you can't time the market.
Don't trust experts telling you to enter and exit.