By Jeff Reeves

One of the best parts about my job is interacting with real human beings who have real financial questions. Last week, I got a good one from a 55-year-old who just got a windfall of $100,000, but never had a penny in his retirement account before this sum.

So ... what should you do?

It's impossible to sum up all the ins and outs of retirement planning in 600 words or so, but here's my basic advice to get you started:

Invest in stocks for growth, investment-grade bonds for safety

A "safe" rule of thumb is to use your age as the percentage of fixed income or bonds you should hold (see InvestorPlace video) -- in your case, 55%. But seeing as you are starting from nothing, I might encourage you to be slightly more aggressive to ensure you grow your money fast enough. $100,000 or even $200,000 won't provide for much wiggle room if you want to retire at 65 and live to be 85.

Keep your costs down

Think about it this way: If you have $100,000, but you pay $2,000 in fees and trading costs and "research," you need to make 2% each year just to break even. If your returns don't justify these expenses, then you're throwing money away. If investing is intimidating, there is nothing wrong with going to a bank or a certified investment adviser to get advice or set up a plan -- but be wary of just giving them the keys to the castle. Sometimes it helps just to pay someone a few hundred bucks and sit down for an hour to discuss your specific situation.

Funds (particularly index funds) are your friend

If you have a basic idea of how to invest, don't feel like you need to craft a crazy portfolio with 20 investments or more. Instead, stick with mutual funds or exchange-traded funds -- preferably low-cost ones that are "passively managed" by being benchmarked to a fixed list of investments. The most popular example is the SPDR S&P 500 ETF (SPY) that charges a mere 0.09% in expenses -- or less than a $1 on every $1,000 you invest. Best of all, it's pegged directly to the holdings that make up the S&P 500 Index. So you get the diversification of all the big-name stocks in there like Microsoft (MSFT), Exxon Mobil (XOM) and Walmart (WMT) -- but you don't have to pay a high-priced manager to pick the right mix. It's built-in diversification, done cheaply. (Microsoft owns and publishes Top Stocks, an MSN Money site.)

Don't overdo it

The biggest problem investors have is that they trade too much or change strategies too quickly. They sell too soon because they are afraid a stock will keep declining, then miss the rebound. They buy a stock too late after it is already up 50% or 100%, then are frustrated when it never moves higher. They pay lots of money for fancy software and active trading … all just to spin their wheels. Research continually indicates that the best strategies are long-term ones, not ones that should change every month based on the whims of the market.

Paper trade before you get complicated

Over time, you may learn enough about the markets to want to branch out from index funds and into direct investment in individual companies. That's great -- but make sure you understand the practical matters of the market before you get over your head. I highly recommend "paper trading" (explained here at InvestorPlace) for a while before making any complicated moves. This involves simply writing down the amount you would theoretically invest and the shares you bought, then tracking the pick over time just like you really owned it. It's often the most instructive way to learn about your investing skills … and best of all, you can make beginner mistakes without losing your shirt in the process!

Related reading

• Don't have $100,000? Well here's how to invest just $1,000 now. (InvestorPlace)
• If you still don't understand the different asset classes at your disposal, Wells Fargo (WFC) offers a great primer on the basics here. (Wells Fargo)
• How to start buying stocks and funds, and all the options you have to do so. (Investopedia)

Jeff Reeves is the editor of InvestorPlace.com and the author of "The Frugal Investor's Guide to Finding Great Stocks." Write him at editor@investorplace​.com or follow him on Twitter via @JeffReevesIP. As of this writing he did not own a position in any of the stocks named here.

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