Build your network - The next thing is that you may have experienced a set of problems in your personal life or work but that set of problems may not be intersecting the set of problems you are suited to solve. It's worthwhile to get in touch with other people and ideally understand their business problems in particular. If you can identify and validate a business problem then you are almost there since you now have a short list of potential future customers or consulting clients, what have you.
Cultivate your solution space - You can start right away at identifying a niche of solution space you are a candidate to solve and try to keep getting better at that space so that you can be on the lookout for intersection between your capabilities and an interesting problem you validate.
Another important note is to be able to discern what is a promising problem and also not what YC calls "tarpit" problems. Tarpit problems are usually in the consumer space and are problems that everyone has like "I can't find a good restaurant" but in fact many projects have come and gone but it's hard to realize because the skeletons of have sunk into the tarpit.
EDIT: to answer original question.
For me personally it had to do with maintaining networks of people I had worked with in the past in order to get exposed to business problems that I wasn't aware of.