Here's mine! I just recently started making the fancy update images; a friend of mine told me they made a noticeable difference in sharing her comic, and I gotta admit I feel really good about how tweets and tumblr posts look with 'em! :>
I find that for the comics I follow, reminders about "hey, did you miss this update?" are appreciated, so I do that too! It's easy for people's twitter feeds to move so quickly that they miss stuff, so you want to mention it a few times, whether that's morning/evening or even next-day reminders.
Something I've seen a lot of people do is reply to their own tweet rather than making a new one -- this bumps the original update tweet up to the top of your follower's feeds because of the way conversations work on twitter. And if you leave the "@" in it, people won't see those tweets on your profile, if that's something you care about!
To people who use hashtags: do those noticeably help? It's always felt weirdly impersonal and like..... desperate-business-y, but I also only recently started participating in stuff like #webcomicchat so there might be a whole bunch of people checking comicking hashtags that I don't know about!!!