Joining different art events, collabs, guest comics is a good way to make friends, participate in the community, and have some artwork you can share with your current followers. Being active keeps you fresh and new.
Also during those times where it feels like your series is experiencing a plateau in growth, it can be fun to try something new like livestreaming, art requests, Q and A's, character bios, extra non canon strips, daily doodles, so on. Just anything to mix it up a bit and get people interested.
Networking and building friendships is extremely important. Try joining the Twitter webcomic chat groups or hangout and chat here on the forums.
Self promotion, because no one else will promote your comic in the beginning. It must be you and you must constantly think about it. Indirect methods, like participating in communities, are more effective than link spamming, however, sites like project wonderful and top webcomic list ( vote for yourself in the beginning) help get your comic in front of more people.
And always just keep drawing and perfecting your craft while remembering to have fun with it.