Some investors gloss over the "ET" in ETF, failing to understand or appreciate what these two letters stand for and the implications of investing in a fund that trades like a stock. The exchange-traded nature of these funds is increasingly taken for granted as many of the largest ETFs trade at tight spreads in very narrow bands around their net asset values through most market conditions.
But not all ETFs are created equal from a liquidity perspective, and investors shouldn't take ETFs' liquidity for granted. Also, the market mechanisms that underpin the ETF ecosystem have experienced hiccups of varying magnitude, ranging from the "flash crash" to more recent episodes of lesser scope and impact. These events have served as painful reminders of why investors should exercise caution when buying and selling ETF shares. Here I provide four tips on how to best trade ETFs.
1) Use limit orders.
If I had to provide just one tip, this would be it. Use limit orders when trading ETFs. Investors tend to use market orders in instances where time is of the essence and price is of secondary importance. Investors using market orders want to execute their entire order as soon as possible. For very large, very liquid ETFs that trade contemporaneously with their underlying securities, like 
iShares S&P/TSX 60 (XIU), market orders will likely result in fast execution at a good price. But most of the roughly 500 exchange-traded products on the Canadian market are smaller and less liquid than XIU and its ilk and may also trade out of sync with their constituent securities.
In all cases, using limit orders is good practice. Limit orders will ensure favourable execution from a price perspective. A buy limit order will fetch the buyer a price less than or equal to the limit price, while a sell limit order will transact at a price greater than or equal to the limit price. What is the potential cost of using limit orders? Time and incomplete execution. That is, it may take longer for a limit order to be filled than a market order, and when that time comes it might not be completely filled. These costs need to be weighed against the cost of being exploited by an opportunistic market maker looking to pick off market orders in thinly traded ETFs.
2) Try to trade when the underlying market is open.
If you are trading an ETF that invests in securities that trade in markets outside North America, it's best to trade the associated ETF when its constituents are actively changing hands in their home market.
For example, it would be best to trade iShares MSCI Europe IMI (XEU) during the morning while European markets are still open. During these overlapping trading hours, it is easier for market makers to keep XEU's price in line with its net asset value, as the stocks in its portfolio are still being bought and sold in real time across Europe. Once European markets close, market makers rely on the fluctuations of the Canadian and U.S. markets as a guide in setting prices, an inherently less reliable touchstone. Of course, some markets that are tracked by Toronto-listed or U.S.-listed ETFs have zero overlap with North American trading hours, like Japan. Investors trading ETFs like iShares Japan Fundamental (CJP) should see tip number one above.
3) Don't trade near the open--or the close, for that matter.
It's best to avoid trading ETFs just after the opening bell: ETFs may take a while to "wake up" in the morning. For a variety of reasons, it takes some time for all of the securities (assuming they trade during normal North American market hours) in their portfolios to begin trading. Before all of an ETF's constituents are trading, market makers may demand wider spreads as compensation for price uncertainty.
It's also a good idea not to trade ETFs as the closing bell approaches. As the market winds down toward day's end, many market makers step back from the markets to limit their risk headed into the close. At this point, spreads tend to widen out as there are fewer actors actively quoting prices.
In light of the considerations above, it makes sense to wait about 30 minutes after the opening bell to trade an ETF and to avoid trading ETFs any time in the half hour leading into the market's close.
4) If you're making a big trade, get some help.
For investors looking to execute a large trade in an ETF, it makes sense to engage the help of a professional. There is no hard-and-fast definition as to what qualifies as a large trade. General rules of thumb would place any trade that accounts for 20% of an ETF's average daily volume or more than 1% of its assets under management as fitting this description. In these cases, investors can save themselves substantial execution costs at the expense of spending some time on the phone with a representative of an ETF provider's capital markets team and/or a market maker.
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