I am not sure what you are looking for, but I will try to give you a brief Idea it might help. Design thinking is a whole some way of looking at a problem. Design thinking are to steps to solve problem, in which we use different tools to better understand the problem and people affected by it.
1. First you have to clearly define the problem with the help of 5 W method (What, Why, Where, Whom, How)
This will give you people and context around the problem you want to solve.
2. after you define are read and talked about the problem and context you can analysis the Collected data with the help of affinity mapping.
3. Start to ideate about the possible solution with the analysis. You can use 'prioritizing matrix' and 'efforts vs impact graph' to valuate your idea.
4. this will help you design your solution which can be again tested with some users to get feedback, complexity level, usability of the solution.
First and foremost, ergonomics is the most important aspect and after this the technical concepts of sound, based on the type of guitar, whether hollow or electric, or any other. Design thinking would be based on understanding of all the mention concepts and revolve around them.