Step 1: prepare your art.
If you are hand drawing the art, scan it, and use a photo editing software to clean it up. I use a combination between Gimp and Photoshop elements, not because Gimp is deficient — it is an amazing product, considering that it’s free and matches photoshop pretty much point for point (though I will say the default included lens flares, a favorite effect of mine, are not quite up to snuff, but I do use an older version than the current), but because elements came free with my wacom, and I don’t use the wacom very often. Also, I don’t have to wait for X11 to start up on my iMac.

I always add the copyright at this stage (which is convenient, as I’m not about to put a comic up here without a copyright)
Step 2: Plan your page.
Determine where you need to add words to the background, for signs and such.

For dialog See where the white space is, and think about the words you intend to use. [NOTE: If you're lettering your own work, this is also a good way to learn to edit. Once you know how much space you have, you must come up with creative ways to trim a sentence away here and there. Alternatively, you could actually do what you're supposed to, and plan the lettering before you start drawing your finished art, but I know it takes a while for that to make it into the process].

Step 3: Get a vector graphics program.
A vector graphics program is really necessary. Unfortunately Illustrator, which is the default, widest used of these programs is around $1000, and if you’re doing this for fun, you’re not going to buy it.
There is a solution, though (one which does not involve theft, admittedly a cheap option, as well), Inkscape. It takes a bit to get used to, like Gimp, but it seems to match up pretty well with illustrator. There are a few things I haven’t been able to find, admittedly, but it will do the job, and it’s free.
Download it!
Step 4: Place the background words first.
The bubbles appear on top, so start with the signs and such first.
If the words go behind someone or something, put them there in their entirety, and then erase as necessary. It’s important to do this, so that if there is a point where the words should appear again on the other side of an object, you actually get them lined up right.

[Note on fonts -- here I am playing around with one of the new fonts I got from comic craft -- destroyer. It was a free font, with purchase of the others. I'm also using Bauhaus 93, which came with the mac, Battle Scarred, one of the Comicraft fonts I knew I had to have, and my personal favorite, Blambot's 10 cent comics. I sincerely recommend checking out Blambot, if you're just getting started, as you can get quality comic typefaces for free to play around with].
Step 5: Bubbles/captions
Place the words first

Then put the bubbles over them, using the circle tool

Set the stroke of the circle, properly.


lower the bubble object


Create a tail for the bubble using the pen tool

Click enter once you have what you want [NOTE: this is the simplest, you can add a turn to it, or make it more impressive, as you desire]
:

Shift select both the tail and the balloon with the selection tool

and merge them using the path > union function

Step 6: I usually create a border around the panels using Inkscape as well as well. Just use rectangles to create a border, and then use the union function as above.
Step 7: Go to File > Export to bitmap (selecting the “page” option)
Step 8: re-open Gimp or Photoshop, and save the file as a jpeg, gif, or something else that’s smaller than a bitmap or png.
And there you have it… it’s not so bad, eh?
See the final product, here.