Advice for someone new to the world of graphic novels!?

I've read: Y:the Last Man, V for Vendetta, Watchmen, League of Extraordinary Gentlemen, Blankets, The Dark Knight Returns, Black Hole, Scott Pilgrim, and i think that's all. I just don't understand...where do i start reading the clics like superman, batman, the green lantern, spiderman....??????? Should I buy them in volumes at a book store, buy them in issues in a comic book store, or find the cheapest deal of boxes of them on ebay...or somewhere else?????????? I also dont quite understand how issues work...could i get on a mailing list, where they send them like magazines??? ADVICE!!!!