Answer guided questions section by section. When you're done, get a formatted business plan outline you can use for board presentations, grant applications, and IRS Form 1023 preparation.
A strong mission statement answers: What do we do? Who do we serve? What impact do we have?
Your vision is aspirational. It describes the end state you're working toward.
Be specific. 'Youth need mentorship' is weak. 'In our county, 40% of at-risk youth lack access to consistent adult mentorship' is strong.