Through observation, the arrangement of the objects frame as a triangle. Accordingly, I used triangle to compose the picture.Needless to sketch too many details, instead painting the right relative location and size of objects are the most important thing at this stage.
The objects can divide the background into 3 independent area. Paint they separately can apparently lower the chance of failure while painting the background. (background dries too quick while painting it, which causes the ugly cauliflower edge.)
Pre-wet the background to extend the drying time of the following washes. Loosely paint the background with the mixture of red, orange and yellow to make it more colorful.The tip is to keep mixing in the different ratio and apply the wet-in-wet technique.
Apply dark colors such as brown on the wet wash to cover the dark area. Don't touch the light part of the objects, but it's OK to paint into the dark side of the objects because the color of background can be covered later. Besides, make the background overcolored to offset the fading after water goes off.
Deal with the objects with the mixture of black, purple and orange, and paint the object on the far left with the mixture of yellow, orange and kinda black. Preserve the bright area. Loosely paint the harrows of the abacus under the desk lamp. Only need to express the feeling of the beads of the abacus.
Deal with the second layer of background with flat headed brush but don't paint the detail of the wood strips. It's OK to just use the color lumps to express the silhouette. Fill the white area preserved with the mixture of yellow and kinda orange but preserve the highlight. Finally, glaze the light yellow over the highlight.
Finally, in order to touch up the work I used the small brush to soak up a little water, and washed part of the bright area to make it brighter.