While a lot of people decide to play defensive during a down economy, that isn't the only stance to take. In fact, a weak economy produces a number of opportunities that aren't always there when the economy is strong.

While your instincts may be to hole up and wait for fairer days, a more aggressive approach can improve your net worth a whole lot better. Here are a few ways to take advantage in a down economy:

Stocks: Warren Buffett's stock-buying strategy has been always been ''Be fearful when others are greedy; be greedy when others are fearful.'' He re-emphasized that stance with an editorial piece in The New York Times last week entitled "Buy American. I Am." Buffett says that due to the fear in the stock market and the attractive prices of U.S. stocks, that's where he's putting his personal money.

If you are in the stock market for the long haul, a down stock market is what you want when you are buying. Year to date, the Dow Jones Industrial Average is down more than 30%, and the S&P 500 and the Nasdaq have lost more than 35% each.

It's much better to invest in the stock market for your retirement when it's having trouble rather than when it's riding high. The only time you want it riding high is when you are retiring so that you can cash out at the top.

Trying to anticipate the bottom is always impossible, so you don't want to wait, but you also don't want to put all your money in at this moment. Instead, begin setting aside an extra amount you can afford to invest on a monthly basis and keep buying with a long-term approach. Your retirement account will thank you for it.

Collectibles: When times get tough, people often look at what they have around the house that has value to raise cash, and that often means raiding collections. The problem is that when everyone is trying to raise cash there are far more sellers than buyers. This means you can often get collectibles at bargain prices.

If you have deep knowledge of specific antiques or collectibles, buying them during economic downtimes can yield huge gains if you can wait for the economy to recover to resell.

Housing: If you have ever been interested in investing in real estate, now is the time to begin looking. While flipping houses for profit is no longer an option with so many on the market and prices continuing to fall, it is a buyers' market. This puts you in the position to name your price, knowing that if it's not met you can simply walk away and there will be plenty of other opportunities at hand.

Research the rental market in the area you plan to buy in, and shoot for a positive cash flow from Day One. If you are willing to do the research, you can cover all your costs and be in a great position when the housing market recovers.

Alternative Auctions: When times get tough, a lot of people lose the ability to pay for things. This results in an increase in bankruptcy auctions, storage-unit auctions and government auctions. Buyers can usually find good deals at auctions, but if you know what you're doing, a bad economy can make the deals even more plentiful. You'll find more auctions and fewer bidders to compete with.

Auctions are just one source of bargains during a down economy. Make the rounds to antique stores, consignment shops, flea markets, second-hand stores and yard sales to find great items to sell down the road at a good profit. If looking for deals on foot isn't for you, classified ads, Craigslist and eBay can also provide some great investments.

Stockpile: All the advantages of a down economy don't have to be long-term ones. You can also take advantage by stockpiling nonperishable foods and other home essentials. By stockpiling those things that you regularly use when you find them at bargain prices, you protect yourself against inflation of those commodities. In addition, a well-stocked house means that you can purchase goods when they are at rock-bottom prices rather than at the price they happen to be when you run out making your money work even harder for you.

Travel: Most people drastically cut back on travel during tough times, so travel can be an excellent bargain. When there isn't enough demand, tourist spots have excess inventory that goes to waste if it isn't sold. The result is often deep discounts from hotels and other businesses reliant on the travel industry.

The excess lets you bargain for lower prices, upgrades and a variety of other perks that might not be available when the travel industry is in good shape. If you have had a dream vacation in mind and have put away some money for it, you might find that it is a lot more affordable during these hard economic times than you'd budgeted for. If so, it may be a value worth grabbing.

It's important to remember that tough times don't mean that all opportunities vanish. By realizing that even in poor economic conditions that leave most people scared, there are plenty of good opportunities available for those willing to take advantage of them.