Screen Design 
Number of Lines/Columns
You should not design views/screens with more than 50 to 60 visible lines because orientation might suffer. Depending on the average number of hidden fields the customer uses, the screen can actually have more than 50 to 60 fields at the time of designing the screen.
Required horizontal scrolling in combination with vertical scolling on a screen complicates the handling and should be avoided. You should not design screens which exceed the standard number of lines and the standard width of 83 columns.
Compression
All screens should be set to "Compression on" by default.
Release 3.0 should be delivered with active compression algorithm, even for standard sized screens.
Field Arrangement
Related fields should be arranged in group boxes, with groups not larger than the maximum visible part of the screen.
To achieve optimum compression, a two-line layout should only be used for fields which are usually not hidden or only together with other fields.
With multiple-line fields, you should position fields which are presumably hidden frequently at the right screen side to avoid "gaps" on the left border.
Any dynamic extensions of long screens generated automatically by the system depending on previous data input do not make sense because they do not always appeared at the same position on the screen. Additional data should be displayed in modeless dialog boxes, by reading the relevant parameters before the screen is sent or by a user-driven screen extension after a pushbutton has been activated.
Loops
On long screens, you are to define only fixed loops and table controls.
You should choose a loop size which allows to display the entire loop on a screen. (If you exceed 21 lines, the Screen Painter will issue a warning.)
If you do not use any table controls, you can optionally provide each loop with a separate scroll bar in the work area.