you have to be very imaginative, write interesting stories, be well organized, be good at drawing, accept criticism, be able to publish frequently ...
You will also have to make a few choices on the software to use, photoshop still being a bit pricey - you might be interested in open-source software - and nowadays they are as good as the leading one.
Assuming you already have a comics in mind, and have drawn a few pages already on paper.
The best route for you is to scan those pages, and import them in Gimp - then to ink them and color them.
By putting the sketch on layer1, the ink on layer3, and the colours in layer2 - you are pretty much set.
Beware though, not to mix layers - if you're using Gimp 2.6 - if you have Gimp 2.8 there is a new lock/unlock feature you might use to prevent editing the wrong layer.
Then when the art is done, you simply add a layer4 for text. Make sure the text is spell checked because Gimp doesn't have this ability.
Image credit : Battle for Wesnoth comics
