Investors, heed this resolution: Don't get cocky
Before you dive into the market for the new year, professionals advise one key resolution: don't get cocky.
"Don't be greedy. You see 30 percent gains and everyone feels like, 'Wow, I'm a great investor. Look at all the money I made this year,'" said Joe Magyer, senior analyst at The Motley Fool in Australia.
"In reality, the individual investor could have bought just about anything and they would have killed it this year," he said.
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By any measure, U.S. stocks have had a stellar year, with the S&P 500 index surging nearly 30 percent, its biggest jump since 1997, outpacing the gains of the go-go dotcom boom years. The Dow Jones Industrial Average tacked on 26.5 percent in 2013, while the tech-centric Nasdaq totted up gains of 38 percent.
"If you are feeling that compulsion, like 'man, I really know what I'm doing.' That's probably the time to hit the brakes and just relax," Magyer told CNBC.
(Read more: What are your work resolutions for 2014?)
"Just to frame what another 30 percent year would look like, that would put the S&P 500 selling at 23-24 times earnings. I don't think you're realistically going to see stocks sell at that level, certainly not in a sustained way," he said.
"You need to reset your expectations. Over the next decade, you're probably looking at nominal returns of 6-8 percent, including cap gains and dividends, instead of the 30 percent that we had last year," he added.
(Read more: Do US equities have room to rise?)
Others echo the caution.
"Our research does show that by flipping in and out of trading markets or trying to time the market is actually counter-productive," Tai Hui, chief market strategist at JPMorgan Funds, told CNBC. "My resolution would be to stay invested, to say long term."
To be sure, Hui advises tweaking strategies for the new year.
In response to one viewer tweet that recommended keeping money in ETFs, Hui noted, "that should be part of the portfolio, but in 2014, when the world is getting better, we are going to see greater divergence and performance within an index."
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"ETFs can be a very useful tool, in a global, macro driven world," he said, but added, "When the world is becoming more company specific, corporate driven, I think the active management path is going to be much more helpful to help extract that alpha from the market."
—By CNBC.Com's Leslie Shaffer; Follow her on Twitter @LeslieShaffer1