layout - How to organize a form with many fields?

Where I work, we have a system that has a screen with several fields. There are approximately 50 fields and all are important and should appear.

//edited in gimp :D

Any suggestions on how to arrange the fields so that it does not look so ugly and complicated?

Answer

For the question's sake, let's assume all the fields are necessary. But it could be a problem of Information Architecture. Adressing it first could reduce the ammount of fields in the form and make it easier. Here is a good article on IA and web forms.

The most obvious "problem" with the form is the lack of rhythm and balance, in fact it is breaking most of the known design principles.

Notice how there are too many vertical lines. This could be fixed by using a grid, and even composing to a vertical rhythm, it would give order to the form.

Last but not least, you could make it into a multiple step form, so not all the fields are displayed at once. Here a Q&A explaining when to use each and here on how to indicate progress.