The goal of grassroots activists is to secure votes for a given candidate. While there are many ways to spread the message of a candidate, one of the most effective means is one-on-one contact between an activist and a voter.
So how do you build an effective and workable list of voters in your local area? It is actually fairly simple and requires some time, persistence, organization and desire on your part. The best place to start is your own neighborhood. Why? Because you should already know many of these people through your regular interactions in your community. If you don't, then start being involved in things whether it is the neighborhood yard sale, youth sports, church events or whatever you can think of. The more people you know on a personal level the more effective you can be as a political activist.
So here is an effective method of building and maintaining a contact list. This can be done electronically of course, but in all honesty using index cards for something like this is just as effective. For the the example we will say that your neighborhood has 100 homes.
1) Make a list of the 100 homes. Use an index card (or file if you are doing this electronically) for each home that you want to target. Get the names of each adult resident of the household. These can be obtained through voter registration rolls, Google, the phone book, public real estate records, etc.
2) With your initial contact you want to gather information. Are they registered to vote? Are they registered Republican? If not then can you get them to register Republican? What are their interests, concerns, etc. Also find out interests outside of the political world and record that as well (do they like to fish, do they have kids, do they attend church). Keep notes on this information, so that as you interact with these folks in the future you can have a good idea of what issues (both political and not) they are interested in.
3) Each time you visit that home record the date of the visit and the reason for the visit. (e.g. May 12, 2012 -- Senate primary) and record the results of that visit. Was your neighbor receptive to the candidate? Did they make a commitment to vote for the candidate? Do they require follow up? Are they a potential donor?
4) Periodically read through your cards, so that they become ingrained in your memory. That way when you see Joe at the grocery store you can remember to ask how he likes his new boat, or how his kid is doing in college.
5) Visit each home in your list for each pertinent election. For Dems & Indys you want to hit them in the primary season early, and see if you can persuade them to change parties in order to support your candidate. For the GOP folks, you want to go to them a week or two before the primary for maximum effect (most people wait to the last minute to make up their mind especially in down ticket races). For the general election you work the entire list again, with all voters treated equally.
So to conclude, you can be a highly effective activists by simply getting out into your own neighborhood, getting to know your neighbors and asking for their support.