Spacing and Alignment
Keep labels short - Be aware that translated English text can expand up to 30% in some languages.
Do not shorten your labels to the point of losing meaning, however. A three-word label that provides clear information is better than a one-word label that is ambiguous or vague. Try to find the fewest possible words to satisfactorily convey the meaning of your label.
When the label is associated with another control, like a line edit, be sure to set the the line edit as the buddy of the label.