There are a few areas of exploration around visual thinking.
The most basic one is developing a visual vocabulary. It’s not actually about “learning to draw”, but to broaden your ability to express yourself visually beyond using words. In this territory I recommend books by Kurt Hanks or Dan Roam. These are the fundamentals.
The more advanced one is the world of information design, which is more about conveying meaning and expressing visually in order to influence. Here the classic is Edward Tufte. If you want to learn how better information design could have possibly changed the fate of the Challenger shuttle, or how a cholera outbreak was stopped in 19th century London by a clever use of diagrams, read his Visual Explanations. Or if you are short on time watch his recent Future of Data Analysis speech.
A great example of applying visual thinking to explore and illustrate ideas is the book Liminal Thinking by Dave Gray. It shows how far this practice can take you on the journey to come up with original thought.
In contrast, I do not see mind-mapping as that useful in the exploratory phase of problem solving and in any kind of emergent thinking. Mind-mapping is really just a tool to organise information. In that sense it’s an analytical tool that helps to illustrate what we already know. It is useful when you want to divide a big topic into sub-categories, but it is not that useful and practical in spotting connections, themes or in synthesis. However this is a personal preference, and I had a lot of people swear by this technique.