The very first thing I would advise is to stay in your area of expertise. If you come from a medical background, I wouldn't advise going into the textile business like I did. Operating a business is challenging enough, so don't add the burden of having to understand the nature of the business in addition to building the business.
No matter what business you pursue, I highly recommend you examine every aspect of the business. If it is a manufacturing business, make sure you fully understand the entire supply chain and appreciate what an interruption in any one of the components can do to delivery times. What has to be fully appreciated is how one delay will get the entire production process behind schedule, not just for one customer, but every customer in the queue.
If you are selling a service, understand the competitive landscape and be certain you are comfortable with how to market your business. Often times in business discussions people equate sales and marketing in the same breath, but I can assure you, they couldn't be more different. Although effective marketing can lead to increased sales, the selling process and marketing process are two totally different functions. I am a great salesperson, but have a very limited grasp of marketing , especially in the social media space. If you are a solo operator, or form a partnership, make sure you possess the necessary skills and experience to launch an effective marketing campaign for your business.
If you elect to go into the retail space, understand the hours it will take and also that in most cases, you are dealing with low wage employees. If you are not comfortable in managing younger workers, I would caution you before taking the leap into retail. Nothing can make a business more stressful than constantly dealing with employee issues if this is something you have never done before and realize it is not one of your strongest skills.
I will end here, as this really is just the first glance at looking at involving yourself with a business, whether thought investment of purchase.
Stay tuned for many more anecdotal stories from my experiences.