As you have a good long-term horizon of 20 years you have a lot of options to invest your money and plan retirement.

You need to diversify your investments across the sectors, so you will be at minimum risk, when you say 20 years the risk is actually minimized and no matter where you invest you will see your money growing, how much it grows and in which asset it will grow more is difficult to answer but 20 years time-frame is good enough to make your money grow in any asset.

You can invest in equity mutual funds, start saving and invest systematically in equity mutual funds, invest your money every month, so you get the benefit of averaging. If you invest all your money in one go, and the next day the market falls, you would be in a loss and kind of feel like losing trust on market. Investing systematically minimizes your risk. Mutual funds rewards investors over a long-term if you see the history, this is because the earnings of companies grow over a long-term where the fund manager of the mutual fund has invested, as he is the right person to put our trust on, and as he is the master in this field. So, invest a part of your investment in mutual funds systematically.

You can also buy property, if you have enough cash with you, and if you are sure that the prices of land in a particular area will rise after a period of time, you can invest and forget and let the change happens and let the prices of land in that area grow. Property investment has turned really beneficial for many investors and it is considered as one of the best investment. So, also invest some part of your investment in property.

Invest your money in gold. As we have discovered the value of gold seeing the appreciation in the price of gold over the last ten years, we can surely say it is a good bet and we are far away from seeing the peak price of gold and it really feels like that. Gold acts as a hedge against currency, it is resistant proof, it stays years with the same glitter and shine. Buy gold in whatever form you like, either ETF or gold bars. If your purpose is just to invest and don't want any theft risk then you can buy ETF, open an account with local broker and he will guide you how to make an ETF investment. ETFs are liquid, if you are in need of money you can instantly sell your ETF units and exchange them in cash.

Also, invest some of your assets in silver, I know silver is driven by a lot of speculation and it makes you wait to see your buy price if you had brought it at a wrong time, but as you say 20 years horizon, it is worth an option to invest. Commodities are bound to rise, as they are going to end one day and hence the price of silver.

So, bifurcate your assets as I mentioned above and you are done.

I also agree with the above answer.

Please read rich dad and poor dad by Robert Kiyosaki and Sharon Lechter, which will give you really good advices.

I would talk to a financial adviser or do research on the topic. There are many good articles on the Wall Street Journal's website under Personal Finance. I learned an easy way to invest in my Personal Financial Planning class. Take your age and put a percent behind it. This should be the amount you invest in stocks. The remaining amount should go into more conservative accounts such as bonds and IRAs.

First, buy insurance.
You can buy whole life insurance, so that when you retire, the cash value of the policies can keep the policies in force.
Some whole life insurance policies allow you to convert them into annuity.
If you find life insurance with such provision, you can buy 2 or 3 policies.
Second, invest in very stable companies that pay dividends regularly.
The dividends will be your income in your retirement. Some companies do not change dividend payout even when the economy tanks.