Lighting
Lighting is probably the most important aspect of a self-portrait, as it directly influences the aesthetic quality of the end product. For instance, a photograph or painting bathed in early-morning or late-afternoon light will create a softer, more relaxed effect, which would lend itself to a more cheerful self-portrait. This does not mean the artist needs to be smiling or depicted as cheerful in such light, but it will likely strike a discordant, or at least odd, note if he is not.
Composition
The position of the subject's head or body is crucial to a self portrait. They could look out of the picture, showing confidence, arrogance, directness or steadfastness, such as a captivating self portrait by Mexican painter Frida Kahlo (Self-Portrait, 1940), in which she stares defiantly at the viewer. On the other hand, the subject's eyes could be downcast, depicting sadness or loss; or they could look sideways, showing loneliness, chastity or a shifty demeanour.
Context
The setting in which the artist is placed is usually a matter of personal choice. For instance, some might choose to show no context, with a bland background, while others might opt for a symbolic setting. In a 1630 self-portrait, Dutch painter Judith Leyster depicted herself in a casual pose while doing a painting of something else. The purpose was to show that she could paint other subjects with the same flair as she painted herself.
Mood
Influenced to an extent by lighting, the mood of a self-portrait is revealing of the artist's personal context. Mood depends on the expression on the artist's face as well as external factors such as a dramatic sky or a dark background. This is not to say that all self-portraits done at night, or in menacing weather, will be downbeat, but such factors usually set a more melancholy tone. In addition, a smiling subject will make a completely different impression from one who is scowling.