First, take a look and see who else is working on the problem you care about. There will almost always be someone who is doing the work you are doing and if it's a good organization, you can volunteer or work with them rather than starting an identical organization.
Sometimes there isn't someone solving the problem you're passionate about and that's where you come in. Maybe your issue is climate change. There are thousands of organizations working on "climate change" but if you are specifically worried about penguins getting caught in plastic bags and no one else is working on that, that's your thing and you should go for it.
It's 2018. You don't need a business plan or a bank loan to start a nonprofit. For most people, business plans are just a device used to put off actually getting started. No matter what you do, you are going to change your process dozens of times before you find the right solution. It's called pivoting and it's what every smart startup does. Your "business plan" should be a working document that clearly states your mission and goals which guide you as you find the right solution.
You will, however, need money. And unless you're lucky enough to have a trust fund or rich uncle, you're going to have to raise it. To start Spread The Vote I crowdfunded on a platform called Crowdpac. I was able to raise enough to work full time for a few months and figure out the right way to build my organization and I have used Crowdpac many times since then. You can also start a nonprofit on the side while working a full time job and, depending on your project, costs can be kept very low.
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