To everyone in the US: If you have a 401(k) and aren't maxing it out your contributions to it (15% income, IIRC), focus on that before
any other investments. Don't bother planning out where to put the money, or which stocks, or which funds. Put it all in the longest term Vanguard fund you can find (30 or 40 year, if possible). If you can't afford to max out your contributions, at the very least max out your employer's contributions (if your employer matches up to 5%, invest at least 5% of your income in your 401(k)). Employer matching is free money, so it's beyond stupid to give it up.
As was said before, Vanguard and other funds invest your funds extremely diversely, which essentially means you're not investing in any companies or industries, but the market as a whole. Year over year changes don't matter. Some years you'll be up, some years you'll be down, but over the course of 30-40 years, the market will be much, much higher than it was when you started, and all your compound interest will have given you a huge amount of money by the time you retire.
If you don't have a 401(k), invest in a long-term mutual fund anyway, for the same reasons. Your employer won't match (since it's not a 401(k)), but the rest of it still applies.
After that, individual investments should be one of two things: Either 1) Extremely safe, low risk stocks like public utilities that pay dividends. You'll never make much trading utilities stocks, but they aren't volatile and will give you a nice steady income (which you can reinvest in the market, for more money!), or 2) Riskier, less safe stocks in companies and/or industries that you genuinely understand better than the market at large does. If you know a ton about drones, to the point where you can reasonably decide what drone technology will do well, what will fail, and which companies will succeed, then invest in drones. If you don't know any more than the market as a whole does, all you're doing is making risky bets that you don't understand. It might work out sometimes, but it's pretty much exactly like gambling at a casino. You might get ahead temporarily, but the house will win in the end if you keep playing long enough.
Things like
this are extremely important to keep in mind. Mutual and hedge fund managers spend their entire career studying which stocks will do well and which will do poorly, and the overwhelming majority of them
still underperform the market. If people with expensive software studying the market all day long can't beat the market, there's no way 30 minutes a day on Yahoo Finance will leave you anything but stunningly unqualified to try to do better than a standard unmanaged Vanguard mutual fund.
There are a few exceptions, of course. Every once in a while a hedge fund manager will discover some secret and make all his investors rich overnight. You hear about them on the news every once in a while. Don't let this trick you, though. The reason it's big news when it happens is because it happens extremely rarely, and almost none of the managers who outperform the market continue to do so for long periods of time.
Investing really isn't as hard as people think. The market performs best 99% of the time, so 99% of the time you should just do what it does, and you do that by investing in a diverse mutual fund over a long period of time. Simple, effective, and proven by time.