Spacing and Alignment: See Form Label Alignment
Language: 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.
Capitalization: See Captitalization
Keyboard Accelerators: See Keyboard Accelerators