You are either losing market share within your category or your category is declining – these are the most common reasons for declining sales.  It is always good practice to conduct a competitive analysis to see if there have been innovations by your competition.  Another good practice is to talk to your distributors and retailers to gauge consumer interest in your product. While you're at it, ask your distributors and retailers what they think of your product.

No matter how clever you think you are, your competition is just a half step behind you.  You must constantly seek new ways to reinvent and innovate.  Orville Redenbacher Popcorn was considered as perfect a popcorn product as possible. What would have happened to Orville Redenbacher if the company let another popcorn product beat it to the microwave innovation?  Be always diligent and never get overconfident.

Often, product managers think too narrowly.  That causes them to chase  rather then create new solutions.  That means they tend to copy what their competition does rather then beat their competition in innovation. The best way to create new solutions is to look outside your category or business.  Look at what other categories are doing as an example of what may be possible within your category. Look at what the squeezable syrup bottle did for ketchup, mustard and mayonnaise.

If your current consumers don't want your product, you can't give it away.  So look for a different consumer.  If the grocery channel isn't working, try the military channel.  If your digital product isn't selling as a standalone, seek complementary products to bundle it with.  Game compilation products at a sharp price are big hits during the holidays.

If you're trying to get your management to continuously invest marketing resources just to hold on the same target consumer, you're beating your head against the wall. When the sale of Tang became stagnant, General Foods used its excess production capacity and invested in marketing to create a new powdered sugar beverage business – Country Time Lemonade.  American Express spent millions on Travelers Cheque advertising during the Christmas holidays not because people were traveling to foreign countries, but because purse snatching and pickpocketing rose dramatically during this shopping period.

The first one NOT to implement is what your competition has already done.  That's a tough row to hoe in a crowded competitive market.  Rather, think big.  But don't swing for the fences without having spent time at the batting cage. Think big, think differently and TEST!

The most obvious is when regulations require it. Another is when the competition has destroyed the category.  A good example is how the iPhone and Android apps storefronts killed the apps storefronts of the telecom carriers. The carriers simply could not compete with the iPhone apps available only through iTunes or the Android apps that cost almost nothing through Google. But when you kill a product, remember that, like a cadaver, it may offer valuable assets that can be reused.  For example, Electronic Arts took the landscape engine used in an old flight simulator game and reused it in a skydiving video game.