Stock investing is filled with intricate strategies and approaches, yet some of the most successful investors have done little more than stick with the basics. That generally means using funds for the bulk of your portfolio — Warren Buffett has famously said a low-cost S&P 500 index fund is the best investment most Americans can make — and choosing individual stocks only if you believe in the company’s potential for long-term growth.
Disclaimer: NerdWallet has entered into referral and advertising arrangements with certain broker-dealers under which we receive compensation (in the form of flat fees per qualifying action) when you click on links to our partner broker-dealers and/or submit an application or get approved for a brokerage account. At times, we may receive incentives (such as an increase in the flat fee) depending on how many users click on links to the broker-dealer and complete a qualifying action.
Choose your trading partner wisely. To trade stocks you need a broker, but don’t just fall for any broker. Pick one with the terms and tools that best align with your investing style and experience. A higher priority for active traders will be low commissions and fast order execution for time-sensitive trades (like our picks for best online platforms for active traders/day traders). Investors who are new to trading should look for a broker that can teach them the tools of the trade via educational articles, online tutorials and in-person seminars (see NerdWallet’s round-ups for the best brokers for beginners). Other features to consider are the quality and availability of screening and stock analysis tools, on-the-go alerts, easy order entry and customer service.

Keep good records for the IRS. If you’re not using an account that enjoys tax-favored status — such as a 401(k) or other workplace accounts, or a Roth or traditional IRA — taxes on investment gains and losses can get complicated. The IRS applies different rules and tax rates, and requires the filing of different forms for different types of traders. (Here’s an overview of the IRS rules for stock traders.) Another benefit of keeping good records is that loser investments can be used to offset the taxes paid on income through a neat strategy called tax-loss harvesting.
Different investors are going to prioritize different things. A day trader, for example, requires speed and flexibility. A first-time trader may value educational resources and reliable customer support. But one thing every trader should care about is cost. Not paying attention to investment expenses is like revving your car engine while filling it with gas. That's why we spent a lot of time balancing price with what each site offered.
When you've been approved for margin stock trading, you're also eligible to short stock. Almost every successful stock trader has shorted stock at one time or another. When you short stock, you make money when the company's shares fall—or, even better yet, when they crash. The problem is that you can expose yourself to unlimited liability when you do this. 

How much money should I invest in stocks? If you’re investing through funds — have we mentioned this is our preference? — you can allocate a fairly large portion of your portfolio toward stock funds, especially if you have a long time horizon. A 30-year-old investing for retirement might have 80% of his or her portfolio in stock funds; the rest would be in bond funds. Individual stocks are another story. We’d recommend keeping these to 10% or less of your investment portfolio.