Having recently formed an advocacy group, I would say the first step is determining the most significant need in your service area. Don't assume it's the same as other areas...do your research, collect data, be objective. For example, some places need spay/neuter programs while others may need more focus on intake diversion or puppy mill legislation. To be the most effective, you will need to fill gaps and take on challenges that are not being addressed. Once you have that information, determine what skills and resources are needed and build your team accordingly. Start small...it's better to build on successes than lose credibility and support as a result of a failure. Commit to learning something every day! There are soooo many incredible resources available in various forms throughout the animal welfare community -- this forum, Maddie's University, Best Friends, ASPCAPro, Alley Cat Allies, American Pets Alive!, Association for Animal Welfare Advancement, many humane education organizations, and the list goes on. Also look for in-person training & continuing education and networking opportunities.
From a business perspective, know what is legally required in your state for non-profits, obtain 501c3 status and create a marketing plan for your "brand". In this age of social media, you will want to have a name, logo & business plan that support your mission statement. And, make no mistake, your non-profit must be run like a business...be fiscally responsible, file reports on time, create a budget, make fundraising goals, maintain your profile on GuideStar.org, include non-profit management training in your learning plan. There are lots of resources for this available, too.
And, perhaps most importantly, be honest with yourself about what you can realistically commit. This includes time, money, skill set & personality. Compassion fatigue is very real.
Attached is an action plan tool from the AAWA that might be useful.
And, of course, wishing nothing but success to any and all who are on this path! Godspeed! <3