There are many reasons for a business to "go south". It may depend upon what market you are in. Some markets fluctuate quite a bit while others do not. Most people believe that their love for doing something is evidence that they should go into business for themselves. This is dangerous unless you also understand the market and what it really takes to start a business.
It is a really good idea to have a variety of customers (large, medium, small sized) and try not to have one customer who you do more than 20% of your business with. The more customers you have, the less financial stress there will be on your company if one should decide to leave.
You may also want to add more variety of products or offerings to your customers. The more unique, the better (for instance, personalized service as opposed to, "take a number".
Usually, a business will dry up for one of two reasons: Lack of customer service or poor products. What is the real reason your business is "drying up"? If you are losing hope in regaining your business cash flow volume, then you need to either: Determine where your resources would be better spent or what you need to do differently to encourage growth in your company. Honestly, sometimes you end up in a slump due to an attitude or physical issues like depression or disease. You need to quickly deal with these in order to succeed in any business.
Location is also a really important consideration. Yes, you may save $500/month by choosing a storefront that is in the back, but how many customers will check your store out if they cannot see it in front of them? This is very important: If you are thinking of starting up a "Brick and Mortar" store in a strip mall or purchasing a business in a good traffic area, make sure you check on what is on the agenda for street, sewer line, water and gas line repairs in front of your location for the next 5 years. I've seen a few companies start up in an area that was perfect. However, since street repairs were scheduled, as soon as they opened nobody could even get close to their store. Perfect recipe for disaster. If you have a purchase or lease agreement, put in the wording, "No payments will be made if the business is impossible to conduct due to this location being inaccessible by customers" and define what that would be for your location.
For me, the most important question is: "Why am I doing this business?" If it is only money, you may be very disappointed. A wise person once said, "If you do what you love, you will never have to work a day in your life."
Lastly, you need to have some mentors who have been successful in business in your industry to bounce questions off of. That is one of the main purposes of the Ambassadors for Business in most towns. They are there to come alongside and help you with making important business decisions. It may also be a good idea to have a CPA firm to help you keep your financial records. You might want to read, "The E-Myth" and "The E-Myth Revisited" by Michael Gerber. I always tell my customers who often ask me to do something out of my scope, "If I was good at everything, I would not be good at anything!". Knowing your limits and admitting them is appreciated by your customers.