Don’t try to time the market.
As tempting as it is to try, it is not possible to time the stock market. People have written millions of pages of research on this topic and NO ONE has ever found a legitimate way to determine its trends.
Use cost averaging.
By buying stocks on a periodic basis (like once a paycheck, once a month or even once a year), you will always be buying at an average price. If you try to time the market, you may be buying at a high or low valuation.
Take taxes into account.
When you buy stocks, try to hold them for more than one year so you get taxed at the long term capital gains rate, which is currently 18%. If you sell your stock before one year, you will be taxed at your ordinary income tax rate, which is almost always higher than 18%, sometimes twice as high.
Invest as much as possible into tax-sheltered 401K, 403B and IRAs.
By investing in tax deferred plans, you are able to invest money and not worry about the tax implications. With 401K and 403B plans, you get to invest your earnings before taxes, so the investment will grow on a higher base. For example, if you received a paycheck for $2,000 gross pay and taxes were taken out, you'd be left with only $1,200 or so to invest. The investment return on $1,200 could be substantial, but if you could invest that same $2,000 in a tax deferred account, you would be investing and earning a return on $2,000 instead of $1,200. Also, many employers offer matching investments that could make that $2,000 investment equivalent to a $4,000 investment. Put as much as you can into these tax deferred investments.
Diversify your investments.
Don't just invest in stocks. It is better if you diversify your investments into other asset classes including real estate (a house), cash (savings account or CD) and maybe even bonds. That way, if one asset class really underperforms, you will have some exposure to the better performing assets.
Diversify your stocks (mutual funds).
When investing in the stock market, don't load up on just one or two stocks. Diversify your investments across many stocks. If your portfolio is not large enough to buy 15 or more different stocks, you should consider purchasing one or more mutual funds to ensure diversification.