Diversify. Diversifying your portfolio is one of the most important things that you can do, because it diminishes your risk. Think of it this way: If you were to invest $5 in each of 20 different companies, all of the companies would have to go out of business before you would lose all your money. If you invested the same $100 in just one company, only that company would have to fail for all your money to disappear. Thus, diversified investments "hedge" against each other and keep you from losing lots of money because of the poor performance of a few companies.
Because ETFs are traded like a stock, brokers often charge a commission to buy or sell them. But many brokers, including the ones on this list of the best ETF brokers, have a selection of commission-free ETFs. If you plan to regularly invest in an ETF — as many investors do, by making automatic investments each month or week — you should choose a commission-free ETF so you aren’t paying a commission each time. (Here’s some background about commissions and other investment fees.)
When it comes to investing, time is your most powerful tool. The longer your money is invested, the longer it has to work to create more money and take advantage of compound growth. It also makes it far less likely that one harsh market downturn will negatively impact your wealth as you’ll have time to leave the money invested and recover its value.

Discounted cash flow (DCF) model: the value of a stock is the present value of all its future cash flows. Thus, DCF = CF1/(1+r)^1 + CF2/(1+r)^2 + ... + CFn/(1+r)^n, where CFn = cash flow for a given time period n, r = discount rate. A typical DCF calculation projects a growth rate for annual free cash flow (operating cash flow less capital expenditures) for the next 10 years to calculate a growth value and estimate a terminal growth rate thereafter to calculate a terminal value, then sum up the two to arrive at the DCF value of the stock. For example, if Company A's current FCF is $2/share, estimated FCF growth is 7% for the next 10 years and 4% thereafter, using a discount rate of 12%, the stock has a growth value of $15.69 and a terminal value of $16.46 and is worth $32.15 a share.
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These extra fees are another big cost to investors, but they aren’t deducted from your account balance. Instead, these fees show up in the price on the ticker tape. That’s why many high-priced mutual funds’ and ETFs’ value per share doesn’t seem to change over time — any growth is offset by fees. Also watch out for mutual funds that charge a front- or back-end load for each purchase or sale. These usually range from 0.5% to 1% and can add up quickly. Warren Buffett: Investment Advice & Strategy - #MentorMeWarren