One of the most important aspects of presentation is alignment and placement of controls. Its theoretical foundation is based on Gestalt psychology. Human perception tends to order experience in a manner that is regular, orderly, symmetric, and simple. Visual impression is generated to an emergent whole based on several principles, called Gestalt laws. Two basic laws are:
Law of proximity: an assortment of objects that are close to each other are formed into a group
Law of similarity: objects will be perceptually grouped together if they are similar to each other
Placement of controls should be carefully done according to Gestalt theory.
Guidelines
Align labels to the right and connected widgets to the left, making a group of form widgets appear to be center aligned. In Qt4, using a QFormLayout handles this correctly for you.
BAD: KDE3 form alignment
GOOD: KDE4 form alignment
Align a group of widgets to the left. This makes use of space more efficiently.
BAD: OSX form alignment
GOOD: KDE4 form alignment
Left align controls over multiple groups (in case of right-to-left languages mirror the alignment). The visual anchor facilitates scanning of content, and left-hand alignment fits as well forms that have been oversized individually.
BAD: no alignment over controls
GOOD: left aligned controls
Keep track on label size; avoid big differences in text length even after translation that could result in much white space on multiple aligned controls.
BAD: Avoid very long captions
In some cases it may be useful to visually separate groups of related options within one group box to facilitate scanning of the dialog. In that case, put a vertical, fixed-size spacer of 16px height between the options.
Separating groups of related options with a vertical spacer.
Align groups of items vertically rather than horizontally, as this makes them easier to scan visually. Use horizontal or rectangular alignments only if they greatly improve the layout of the window.
Create a buddy relation with the caption so access keys are assigned.
If activating a choice affects the appearance or the enabled state of other controls, place them next to it with a space indentation.
If the control appears in a dialog or utility window, consider making the window and the control within it resizeable so that the user can choose how many items are visible at a time without scrolling. Each time the user opens this dialog, set its dimensions to those that the user last resized it to.
For check boxes (and radio buttons as well), see the special guidelines at the appropriate page.
