Well, you don't need a program for that

Just plan the layout of your panels first. The problem here is, that he just drew what he had in mind.

There are lots of good books in German that teach you that. PM me with your email and I'll give you a list of the books I have on that topic (which are quite a lot)

You could also try amazon.de, just make sure that you don't get anything form Christopher Hart

There're also some booklets on Mangas that are quite good and give a lot of tips on panel layouting.

Hm.. but if it's just panel layouting, I should be able to give you a short summery (with example layouts)

Try this:

{"name":"panel.gif","src":"\/\/djungxnpq2nug.cloudfront.net\/image\/cache\/0\/1\/0159451885d518d55530cfec746935bc.gif","w":817,"h":500,"tn":"\/\/djungxnpq2nug.cloudfront.net\/image\/cache\/0\/1\/0159451885d518d55530cfec746935bc"}

Also, the layout of the images needs some work. Centering stuff looks boring. In the first panel, if the walker is more on the left, it would show more how much way is before him and that he has just started the travel, etc.

A program that can give comics a professional look? That is the most secret of John Romita Jr., Todd McFarlane, Masakazu Katsura, Iván Sarnago Jr. and all we professional drawers... If I told you I should kill you then...

Ok, serious: try to find any book about how to draw comic books. Christopher Hart has some nice ones. Since it is the story of a samuray, try to find "Hetappi-Manga Kenkyujo" (may be "Manga Workshop") by Akira Toriyama.

A program that can give comics a professional look... Just live to read this...

I want to add to the great recommendations in this thread:

Comics are drawn 1.5 or 2 times bigger than their intended publishing size, to allow more detail.

You should always use a pencil layout to minimize errors, and never ink over the pencils directly. Some professional drawers scan their pencils, change them to blue with Photoshop and print the blue layout for inking. That way, when the inks are ready, they scan the whole drawing again and drop the blue layer, effectively erasing all the traces of pencil.

Inking must be done with India ink. Most professional artists prefer to use a brush, but for beginners it might be hard to control, a crow quill pen is better in those cases. Inking is quite difficult, because you need to learn to spot blacks correctly and give value to the lines.

Most professional drawers recommend to layout the dialogs first and then align the drawings around. That's why you should have a full script of every page before doing any drawing. The dialogs will help you plan the number of panels and their positions.

Remember to use diferent kinds of shots in your panels; using the same shot over and over again makes your pages look boring.

I recommend reading We3 by Grant Morrison and Frank Quietly to get a grasp on how powerful can be an original use of panels an shots. A comic is a story told in drawings, the reader must understand what's happening with little help from the text.

You might also look for very early comic strips done by current "masters" such as Charles Shultz. Even the greatest had to improve over many years. I guess this reply isn't "how to make it better now" but rather a recommendation to lighten up on yourself.
Unless you've already been drawing every day for 10 - 15 years, of course

Uh, yeah I know Shultz passed on a few years ago. IIRC he specified that no more Peanuts cartoons should appear in newspapers, somebody got around that somehow.

Some artists digitally 'ink' their scans in Photoshop - there are lots of tutorials on this and it can be done to great effect.

I always draw my comics with a black pen, then I scan them to the computer using the black/white option (1 bit color depth).
After that I color the images (GIMP2), then I scale down the whole comic.

Look at this: http://oncer2.on.funpic.de/comicviewer.php?id=6&page=1
Yeah, it's a few years old, and I'm not very talented in drawing, but you can see that the technique I described actually works.

Simon Parzer