Anything unclear or ambiguous? Is the main emotion clear? Is the subject clear?
Anything crooked? Use liquify to fix oddly angled things. Anything too small/too big? Use liquify to adjust.
Try sharpening the artwork. Copy the whole drawing to a new layer, and filter>other>high pass (10 pixels). Set that layer to soft light, or other blending mode.
Do you need to add a film/photographic feel to the image? Create a 50 neutral grey layer, and set to overlay. Add noise.
Do you need an old/decrepit effect? Copy the lines, set the threshold pretty low, and color the layer red to add a messy, rusty effect to the lines.
Do you want more color complexity? Pull up color balance, and play with colors in shadows, mid-tones, and highlights.
Do you need to add depth of field? Light beams? Punch up colors? Deepen shadows? Does it need to be in a particular aspect ratio?
Do you need a fill light layer set to multiply?
Do you need more color variation? soft light brush or color brush, color pick from the drawing and add complexity and variation to other areas
Do you need to use soft light/color dodge/multiply soft brushes to add pops of color or color tints? Play around, it can lead to lovely polished effect. Pump up light and shadow subtlety, add color complexity.