I throw this thread around a lot, but it's got quite a few good self promotion pointers:
The tl;dr version is abuse the heck out of social media for promotion though xD Talk about your comic, share you comic, alert people of updates, etc. On some platforms (notably Twitter) even just including comic-related tags on your post gets some pages to automatically share your comic posts as well. Either way, social media promo is at least good for driving views. Which don't necessarily translate into subs, but it doesn't hurt either~ Other things include networking (things like cross-promotion with other creators, or just making friends who then might read your comic) & other unusual methods like @Jessisheron shared here: