Often, as entrepreneurs, when things are going poorly, we tend to think the problem is with our marketing, or with our sales process. Latch on to the right marketing plan, goes the thinking, or improve our sales funnel, and customers will start pouring in. 

If you've had success (i.e. growing revenue and profitability) in the past, this may indeed be the case, and you may just need some improvements to your marketing or sales funnel.

However, for most struggling businesses, problems with profitability and finding customers usually stem from a poorly thought out business model (for a fantastic, in-depth read on business models, check out this article from Harvard Business Review).