Some people argue with me on this, but I stick by it. I believe the Golden Rule of webcomics is this: update regularly. I mean, being a worthwhile read helps too, but interest in your work tanks terribly when you disappear for periods of time. It's SO tempting because you have no boss cracking the whip on your webcomic, demanding a comic by Friday or whatever, but if you can at all manage a regular updating schedule, do so.
I've been going since 2011 as a webcomic, and I missed one weekly update early on, when my basement flooded. Other than that, I've updated every week. And by and large, I've watched my readership steadily (albeit very gradually) increase.
So yeah, avoidance of long breaks is (in my opinion) a very good thing. Sadly not always avoidable, though.