Do yourself a favour; invest in an index. Don't play the stock picking game. The human mind works against you; everyone is convinced that they can beat the market. If it's even a skill (and it doesn't seem to be) it's a vanishingly rare one even among investment professionals. It's very tempting to think that you could be the next Warren Buffet, but honestly, you're about as likely to get a gold medal in the next Olympics...without training. Resist that rabbit hole!

Having said that, here's some tips if you're going to try and pick stocks anyhow:

0) Don't listen to any tips you see on the internet, including these. If they're actually any good (and not just part of a pump n' dump scam), they'll already have been taken by everyone else. (Honestly you're probably better off shorting anything you see recommended in a public forum.)

1) Pick investments that are likely to go up and down at different times. If you want to invest in an oil company, also invest in an airline; they often go up and down opposite each other. (Note: Again, any obvious tip like this has been exploited to the point that it's no longer helpful. See para 1, above.)

2) Your career is also an investment. Don't, for the love of god, invest in the company you work for. In fact, don't invest in any company that is likely to go under around the time you get fired. Work for Amazon? Invest in Barnes & Noble. Or anyone else you can think of that might do well if Amazon does poorly, and visa versa. And make sure to toss some money at foreign investments; if your country does poorly, maybe some other country will do well.

3) Spread investments out as broadly as possibly. Don't be stupid and say "hey, the whole market can't go down at once!". It can! But it's less likely than a single stock going down, and this is a numbers game. There's never ever a sure thing, but if you can just be a tiny bit smarter than everyone else, it'll pay off in the very long term. (The easiest way to spread investments out is an index. See para 1, above.)

4) And don't just spread your investments across an industry, or a stock market. Try and split investments across multiple asset classes. Stocks, bonds, commodities, foreign stocks, etc. (Via multiple indexes. See para 1, above.)

5) Fees will kill you. Anything with active management is more expensive than its worth. Yes, all active management, no matter how good their track record. At a micro level, past performance is no predictor of future results, and at a macro level past performance is actually negatively correlated. A very common pattern is to do better and better until you do so badly that it wipes out every gain you've ever made (e.g., the entire hedge fund sector when the financial crisis hit). (In other words, see para 1, above.)

6) On a similar note, don't be too active in managing your investments yourself. Reacting to every little dip and spike will waste your time and attention, rack up huge fees, and guarantee bad results. Once you've figured out your strategy (hopefully involving index funds), figure out how much you can save per paycheck, and just do that, with as much automation as possible. Maybe your strategy is "save 20% of every paycheck, with 2/3 going into an S&P 500 index, 1/6 into foreign stocks, and 1/6 in commodities". That may be a terrible strategy, but it doesn't matter if you can just stick to it, and (this is important) don't check to see if it's working for at least a decade.

7) Individual investors persistently WAY underperform benchmarks, because of timing issues. They will hear some hype about a stock, or an asset class, or the idea of investing, and they'll enter the market at or near the peak. Then when things go pear shaped they'll panic and exit, locking in their losses. It's routine for "the market" to have a higher return than the average investor gets; often much higher. Unless you want to lose all your money, don't follow the herd. Your best bet is to just leave your investmens alone (in an index fund) and don't even look at them. If you can't bring yourself to do that, then be as contrarian as possible. If everyone is talking about how awesome gold ETFs are, or the growth potential of tech stocks, get OUT. On the other hand, if a sector crashes, buy!

8) Finally, one more bonus tip: Go for passively managed index funds. (But if you really want to pick stocks, go for ones with low volatility.)