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If you already have a social media presence, start talking to your followers about what you're working on. If you don't, get building! Talk about what you're doing and other things you're interested in, especially in genres related to your comic. Start reading and commenting on other comics you like, and promote them on your blogs etc. Social media only works if you are social - you can't just post a link to your comic and expect anyone to see it. But if you attract people interested in your genre, they'll be more likely to check you out once you debut.
Just posting to Tapas will only take you so far. Make sure your icon is attractive and shows off the art well. Make sure the series is tagged and categorized correctly. Join in on forum discussions.
Or, you don't have to do any of those things! There's nothing wrong with focusing on just Tapas and gaining followers that way. It's best to put in whatever level of involvement you're most comfortable with so that you can remain consistent.