Hello. You could start by doing a diagnosis, or just observing the bands or players and see where they could improve. Another way could be to ask them what they’d like to learn (Allen and Sites, 2012).
When you have an idea, you could first determine what skills do they need, and based on those skills, derive theoretical knowledge (Allen and Sites, 2012). That last part is useful for avoiding filling them with a lot of knowledge that doesn’t translate directly into skill learning (Allen and Sites, 2012), but in my opinion, it might be useful, but perhaps not as much in some cases.
When you have the content, you could design a learning/teaching strategy. For example, there are learning techniques that could be part of such strategy, like emphasizing speed for tremolo development (like Troy’s work, 2021, or other motor learning studies in different skills, such as Frazier, 2002) chaining techniques for motor learning (see Lilly, 2020 and Ash and Holding, 1990), memory palace for learning sheet music or a melody (see Beyond Practicing and Become a Superlearner courses), speed based simplification for gradually speeding up (see Magill and Anderson, 2020) if the physical mechanics allow it, so as to avoid things like fast string hopping, etc.
References
Allen, M., & Sites, R. (2012). Leaving ADDIE for SAM: An agile model for developing the best learning experiences . Estados Unidos de Norteamérica: Association for Talent Development.
Ash, D. W., & Holding, D. H. (1990). Backward versus forward chaining in the acquisition of a keyboard skill. Human Factors , 32(2), 139-146.
Frazier, T. M. C. (2002). The effect of instructional and practice sets: Emphasizing speed vs. accuracy in learning the overhand lacrosse throw* (Publication No. 3044915). [Doctoral dissertation, University of Virginia]. ProQuest Dissertations and Theses Global
Lilly, K. (2020). Chaining Techniques: A Systematic Literature Review and Best Practice Recommendations [Master’s Thesis, St. Cloud State University]. The Repository @ St. Cloud State. https://repository.stcloudstate.edu/cgi/viewcontent.cgi?article=1085&context=cpcf_etds
Magill R., & Anderson D. (2020). Motor learning and control: Concepts and applications (International students edition). McGraw Hill. VitalSource Bookshelf Online
Troy Grady. (2021, mayo 11). Instant picking speed! 210bpm on the second try. What does a “good” first attempt look like? [Video]. YouTube. Instant Picking Speed! 210bpm on the second try. What does a "good" first attempt look like? - YouTube