Crit

(look for elements and traits that repeatedly appear)
The dominating darkness provides a visual foundation for the contrasting lighter figures. The few light and rich colors jump out easily against the dark. ( Dark dominant value)

The figures are composed as though on a shallow stage — all is happening in a narrow, confined space — unified and contained by the wall behind them. The wall is parallel to the picture plane — we're looking straight at it — thus is fully "flat" to us, severely bounding space.

Chromatic color is predominantly warm, where chromatic color occurs. The only cool colors are very subdued — almost gray.

All of the action is bounded by a horizontal rectangle —  the figures generally fit within that contained space. Also, lighting and continuities along the leftmost figure to Socrates' arm build a wide, flat pyramid, as well — a sort of stable compositional form.

In terms of narrative, most of the figures express grief or sadness or dismay — consistently negaive emotions — except Socraties who points upward to higer values. Also, all of the figuresa re men — except a departing woman in th edistance.

(look for alignments, structures or groupings that organize parts into larger entities (gestalt))
There is a kind of pyramid or triangle structure into which the figures are arranged, create a unified mass or grouping.

(look for contrast of any and every kind. Look especially for similar forms that are varied in some way. Look for anomalies — patterns or norms that are broken.)

The intense light areas provide the main visual contrast — they are strong because the image is so dark overall. Socrates in particular is wearing a white robe. His flesh and the robe are well illuminated and so of a contrasting high value.
Notice the varieties of gestures and expressions among Socrates' friends. He, in particular is bold, confident and unafraid — active, lightened, and facing us.
Socrates alone is facing us, as he is also facing his death.
The illuminated action at the right is balanced by a deep-space area on the left — as friends (and Socrates' wife) depart, she looking back. That dark, but deep area offsets the shallow but active and illuminated right side.

The principle of organization may be seen by the placement of the man, Socrates. He is near the center and the placement of the group is natural and balanced. His figure is well-illuminated — his torso is a broad, light shape against the dark, simple background. His figure turned fully towards us — the only figure not turning away. His distinct, open gesture contrasts with the closed, tight forms elsewhere — he is active and extended in contrast to the other passive figures. The other figures have their backs to us, or are in profile. Further, the action (subject) is that of taking the cup of hemlock (poison), and thus accepting his own execution. His left hand is raised, pointing to the eternal truths of heaven -- that which he stands for, even as he dies.
The man with the bowl in his hand is directed towards the man raising his finger directing your attention there.
Along with the other men with their faces and attention pointed towards him. These aspects help direct the eye to the main figure, reinforcing its graphic prominence. 
The background-wall has a sort of spot-light effect, leading toward Socrates. The arch on the left and the dark triangle on the right frame that directional lighting.

In David's Death of Socrates the emphasis is established by the man in the white robe pointing his finger to the sky. His body is very prominent and the only one almost completely square to the front, and because also of his emotion presented is excited and alive.
Note the carefully placed, heightened contrast of lights and darks…large areas of white and of light color are bounded by sharp, crisp edges against dark background.
Note how the other figures “disappear” when contrast is subdued.

Other focal areas include the group to the right of Socrates, the two figures to his left, as well as the figures that are leaving in the distance, framed by the arched corridor. (though arches and barrel vaults would have been strange in Classical Athens.)

Relief areas are be the extensive dark "white space" that makes up the background. The walls and floors are clearly quite subdued — very little contrast or detail.

Such well-established relief areas help preserve emphasis for the main characters.