There are three steps between you and your readers:
You can also sell your books at comic conventions. I can't recommend this strongly enough. Getting a table and getting some face-to-face time with readers will go a very long way towards getting your book into their hands.
Wizard Magazine keeps a pretty comprehensive list of upcoming comic conventions -- they're an excellent place to find comicons in your area.
For the cheapest form of distribution, never forget the internet. It's one of the most powerful -- and inexpensive -- tools at your disposal. Get a website up as soon as possible and set up a secure way to take money from people. I use Paypal, and have been very happy with them. Go take a look at my store to see what an Paypal store looks like. They're extremely easy to set up -- I did mine all by myself.
Webcomics are also an excellent way to promote your books -- you give away the content for free on the web and then sell the graphic novel after you've built up a loyal following. This approach has worked very well for the likes of Fred Gallagher's Megatokyo, Shaenon Garrity's Narbonic and Derek Kirk Kim's Small Stories Online, the latter of which won both a Harvey and an Eisner award.Personally? I don't advertise that much, and I've done well for myself. With the exception of a few banner ads on the Sequential Tart website (which is more just a reminder to my friends that my new book is out, since I'm not only a contributor to the site, but a regular visitor to the message boards), I don't do any external advertising at all.
I know people who dump literal thousands of dollars on full-page, full-color ads in Previews, but I'm too broke to even consider spending that much money on an ad. Instead, I'd take that same money and print a thousand extra copies of issue #1, and give them away as free advertising. Drop a stack of them at your local comic shop. Get together with Diamond and do a free issue for Free Comic Book Day. If you want people to buy your comic -- especially if they've never heard of you before -- give them one of your comics. Not a flier, not a poster, sticker, postcard or bookmark. Save that money you were going to spend on pencil toppers, action figures, tee shirts or travel mugs and dump it into your book.
You shouldn't be making brickabrack for something nobody's heard of yet. Once you get established, then sure, go ahead and order five thousand plushies of your cute little dragon sidekick. Till then, you'd best concentrate on making your books the best you can make them -- a good book sells merchandise, not the other way round. Nothing torpedos a new company faster than dumping a bunch of money on twaddle that doesn't sell, and nothing makes a book sell better than an excellent story. To quote my heros over at Pixar, "Story is King." Until you've made your story the biggest, brightest and best you can make it, everything else is secondary.