Here's a video from Morningstar. The interviewee is Christine Benz, who is a Morningstar executive. She's one of my favorite financial thinkers. Does an excellent job of presenting investing in general and various investments in particular in a way that anybody can understand.
In this video (which also has a text transcript you can simply read), she discusses what people between 15 and 35 years out from retirement should be doing.
For this age cohort, Benz recommends a portfolio of 90% stocks. I have no problem with that, and provided you've accumulated a 3-6 month emergency fund in cash or money market accounts, I might go higher.
One quibble -- Within the 90% equity allocation, she recommends a 60/40 split between US and international stocks. I think 40% international is too high.
The reasons are for my position are:
(1) The largest US-headquartered companies also have huge international presences. So there's a fair amount of international diversification just baked into the S&P and even NASDAQ or Russell index funds.
(2) The demographics for most European and Asian countries are not good. Way too few young people. Which isn't hurting so much right now, but will become more and more painful as time goes on and the OFC dies off. Which is a big issue if you're investing with a 15 - 35 year time horizon.
The US isn't perfect on this, but has Mexico as both a market and source of labor. So temporary immigration policy notwithstanding, we are more insulated than Germany, Italy, the UK, Scandinavia, and even France.
(3) In so-called Emerging Markets, it's kind of like going to Las Vegas. You'll have a few winners and the risk of a lot of losers. Mainly because the political situations in these countries aren't exactly stable. So the threat of nationalized industries (IOW, the government stealing your company's assets by force) is high. As is the threat of civil wars, other unchecked violence, and questionable enforceability of contracts.
So I just don't think the potential returns of Emerging Markets are worth the risks.
So sez me. The fact that I don't agree with Ms. Benz on every single point doesn't mean she's not offering really good advice. The interview is definitely worth your time.