- Rent something out: I had a friend who had bought the giant puppet plant from "Little Shop of Horror" for a couple hundreds of dollars, and who rented it to local productions around his area. He was reimbursed the cost of the plant the first time he rented it out, and anything he made from it afterward was all for him to keep. He also knew how to work the plant so some of the theatres hired him as well. I had another friend you had bought a house and rented out two of the rooms in there, which payed for her mortgage. You could rent out any piece of equipment too: sound system, keyboard, drums, etc.
- Have people work for you: For example if you work for events, you could create a list of musicians to offer to your clients, and charge a price for your work as a contractor. If you already have tons of hours in your private studio, hire an extra teacher to take on even more hours, and keep a percentage of the transaction. It may look like such easy money at first that it might feel like you're taking advantage of people, but this is exactly how the world works: you offer work to someone and they increase your bottom line. It's a win-win situation.
- Sell something: for musicians the most obvious asset to sell is a cd. Cds are so cheap to make these days, and once they're recorded you can sell them at your concerts, on cdbaby, itunes, etc. If you're a teacher you can make your own method and sell it to your students, and show it to other teachers to see if they would want to use it and have their students buy it.