As with any goal you need to set the bar at those things that are actually doable and build upon them. Tasks must be realistic. They must also be measurable with some kind of reward each step on the way.

For example, maybe you might start with something simple you can easily remove yourself from should it be difficult. I speak of things like a visit to a library or a quick stop at a gallery. Basically I would start with a situation you can control that does not yet require social interaction. It ought to be something that simply gets you in the vicinity of people. Maybe then take yourself to a place like a mall where you can sit and observe people and their interactions with others. Work your way up to a situation where you directly communicate with someone. This could be as simple as a worker on a sales floor. And continue from there. Remember though to keep these situations ones you can escape from if necessary (you can always back your way out of that gallery or store for instance). Finally, place yourself in a social setting. Rewards? Maybe a fancy coffee. Perhaps a book from that library. Treat yourself then to something that is different.

Evaluate each step of the way. How will this help me to achieve my goal? Has performing it drawn me nearer? What was successful? What can I work on and change?