There are a large number of options available to the would-be organizer. The difficulty in starting your own grass roots group doesn't come from a lack of options or a lack of issues -- or even a lack of possible support from some kind of larger group which would be sympathetic to your efforts -- but the place where the would-be organizer gets caught, I think, is in the starting and in the continuing. This post will be about the starting.
As I mentioned before in Organizer Pedagogy, what you choose to do should be tailored to your local conditions. But that's not a helpful way of stating things when you don't have a teacher on hand to get started. What counts as "local conditions"? In what way do they matter? How does that help you choose correctly? I think it important to highlight that your local conditions make it difficult to give advice on where to start. But the lesson to take from this, I think, is to be open to changing your plans as you collect people together. They likely have good points, and have things to teach you. An organizer collects ideas from people and willingly implements them, and tries to find ways to make groups work together in spite of their apparent disagreements. They don't have a grand vision to impose on others (even if you do have a grand vision or goal which drives you, you have to be open to other's grand visions and goals, and move with the tactics proposed)
However, these are good rules to think of after having started, and once you're in the process of moving towards goals. In the beginning you need structure. You need a plan. You need an idea. And, you can't impose that idea on others. You can only tell people the idea and look for people that think -- to some extent -- that it's a decent idea.
This is step 1: Forming a core group.
A core group is a group of people that care about an issue -- local or national -- and will be willing to follow through in setting up events. You'll find many people that agree with your idea. You won't find as many people -- perhaps very few out of those who do agree, in fact -- who are also willing to follow through in doing. Ideas always sound cool. Work is. . . well, work. And the work is what you need a core group for -- the core group brings new ideas, allows you to distribute out tasks, and allows you to pool resources and contacts to get things done.
What does a core group do?
A core group sets up community events. For example, suppose you want to educate people on the poor in your community so that they'll get together for a food drive. For that, you'll need fliers to tell people about the event, a speaker who can educate those who show up, and a list of people who promise to bring food to such and such a place as well as to ask others in their respective circles to bring food to the drive. For that you'll need a date, a time, and a place. You'll need to secure that place at that time by talking to the person who owns the place and securing permission. Do this by showing the owner your flier which you'll be passing out, and explaining the goal of your food drive as well as the problem that the food drive is meant to address. Once you have the owner's permission, begin fliering in the neighborhood where people tend to congregate (city halls, churches, schools, public events, parks). Do this by telling the person you meet in the street that they now have a flier. I always say, in a friendly tone, "Here, have a flier!" It's better to say this than to ask, because you don't get as much out when you ask questions. Then, have the event, and have a location where people can bring food, and after the fact let people who donated know how much food you gathered and how its helping out the hungry.
Any of these tasks -- from talking to the owner, to fliering, to speaking at the meeting, to making the flier -- can be distributed out through your core group. That way you're not the only one doing the work, and don't get burned out, and you have input from multiple sources on how it will be carried out (usually making it better), and making it so your resources aren't the only ones going into the project.
That's what a core group is for. That, and drawing strength from one another so that the things you're doing -- when they seem hopeless and worthless and not effective (and there will always be times when you feel this way -- will continue to be done. Burnout is a serious problem. And, it's good to have friends in doing these things so that you can combat burnout.
The strengths of a core group make forming a core group the first step of community/grass roots organizing. Find responsible friends who care about the issue, and meet once a week to discuss what you can do, whose going to do what, and holding each other accountable for the doing.