If you have the guts to buy a stock, presumably you've decided that the stock is at least relatively cheaper than its competitors, or stocks in general. Whatever the insight to that decision should be "reverse engineered" allowing stocks to be identified as unattractive, and thus likely to underperform your picks. There has to be an applicable symmetry to your investment process, otherwise you are deluding yourself that you can pick "winners", if you can't pick relative "losers" as well.
So, to hedge market, sector or industry exposure, look at your current positions. What competitors did you pass up to buy, and why? If they didn't look so attractive then, and if they've lagged since you've had your competing position, then maybe you just proved that you had relative valuation insight as well as absolute. Consider expanding your investment insights to selling short stocks that don't meet your investment criteria - if you want to lower your market exposure. If you're purely bullish, stand pat, or consider higher beta stocks that you like to get that extra oomph.
The purest expression of stock selection skill is to both buy and short stocks that you believe are mis-priced, and earn a spread between the longs and shorts, independent of the market's direction. Give it some thought. You can see how I'm doing with my long/short portfolio on Vestopia.com.
Source: The Advantages of Short Selling