I don't have advice for the charter aside from focusing on defense of any left actions you want to do. Think about what you could theoretically get attacked with. Right now we'd think, "Zionists would call us antisemites for having solidarity with Palestine", so it's useful to have anti-colonial language in your charter.
Overall, my main advice is to be involved, well-liked, and to create agitational situations. Not because you are personally agitating, necessarily, but by recruiting this group into actions that reveal the nature of reaction and capital. Go to a pro-Palestine rally, put up some signs that will get torn down. Organize against the cops. Go to a picket of striking workers (preferably younger workers like Starbucks or other retail). Find a principal that is a bridge too far for local liberal politicians, push for it, and make your group watch their favorite politician lie about them. Let's say, guaranteed housing.
These agitations are a great excuse to hold discussion sessions, teach-ins, and reading groups. You'll have to introduce what you want people to think, otherwise they'll find the Naomi Klein explanations instead.