OK. So you're now a not-for-profit corporation. You are putting all income and expenses through the corporate bank account. You, of course, are continuing to grow your ensemble artistically. Now you are ready to start applying to government agencies and private foundations for support for the things you do for the public good (yes, offering the community high-quality arts services is valued in some circles). Keep in mind that almost no one will give you money to support your desire to play music. Instead, you need to think of what services your ensemble can provide to the community.
Most funding organizations want to see that you have other sources of support — they need to see that you have a way to succeed without them. They will want to feel that you are leveraging their support. For the most part, a good grant application should show one third of the total cost of a program coming from earned income (ticket sales, program book ad sales, etc.), one third from private giving (individual, business, foundation sources), and perhaps one third from all government sources combined. The ASQ generally showed far more earned income (this is good) than government support, and today there is far less public money than we were were starting out.
Start by finding out which LOCAL governments and foundations fund the arts. Read their guidelines. Never write a grant for something you do not want to do. Just because there is a grant application to fund transcriptions and performance of the complete works of The Archies (the rock band from the cartoon TV show, The Archies, including the magnum opus "Sugar, Sugar, You Are My Candy, Girl"), it may not be in the best interest of your group to apply for that grant. You may get funding and actually have to spend a lot time and ensemble effort fulfilling your unfortunate promise. Instead, decide what you want to do with your ensemble, and then go searching for funders that want to fund what YOU do. In addition, grant readers are more likely to fund projects that they perceive an ensemble is passionate about, and that seems to further the heart of the group's mission.
Know that most funders will NOT fund your first grant request to them. Since you have not applied to them before, they will want to see if you are still around to apply in subsequent years. Use the first time application as a way of introducing your organization. If you are rejected on your first try, use it as an opportunity to learn more about the process and the funder. If possible, contact the funder's staff to find out what they thought were the strengths and weaknesses in your application. Make sure you do not put them on the defensive. Thank them for their work, and make sure your next application to that funder reflects what you have learned. Also expect that the first year you receive funding, the granted amount will probably be much small than your request.
When writing for funding from local governments (your village, town, city, or county), first find out what public money might be available and what, if any, arts support they already give. Then make appointments and get to know your political representatives. If you can make your case for how your ensemble can provide cost-effective, high-quality services to their constituents, you are well on your way to establishing a mutually beneficial presence in your home community.
Once you have a track record of successfully completing local grants, use that experience to attempt more regional and national grants. Remember, something that is beyond your ensemble's grasp at an early point in your career may soon be attainable.