Bad/good decisions making
This is the most common reason why business fail as just one bad decision can be a reason for you business failure or success. Decision making is one of the most wanted skills in business and you can learn how to make good business decisions. There are many books written on this topic if you want to improve your decision making skills. Tips on decision making: when making decision do not rush, take some time with every decision and try to analyze advantages and disadvantages of your decision. In beginning this process will take more time but wit a little exercise you will become better.
2) Lack of business experience
You can be the best tradesman in your trade but if you lack some basic business skills you basically have two options: improve your business skills or find some employment. Being in business requires you to have great communication skills, selling skills, some accounting skills, some understanding in general laws and to be passionate about your product or service. This can be learned and the best advice here is to find a good accountant and create a long term relationship with him/her.