Quality of bokeh depends on the quality of the lens (certain intangibles plus things like number and type of aperture blades), aperture chosen, subject-to-camera and subject-to-background distance, and the nature of the background.
If you want nice, rounded circles, you'll want to shoot wide open. The 1.8D has 7 straight blades, so as you stop down, you'll see those octagons as in your example - which might be fine if you like that look, or it works for a particular image, but generally I'd shoot wide open.
Besides aperture, you can increase the blur of the background by moving as close to the subject as possible, so that the ratio of the distance from the camera to subject becomes much smaller than the subject to background. Fortunately the lens focuses quite close, so move in as far as you can.
Although it's subjective, I think the most pleasing backgrounds for bokeh are fairly plain, with little detail, not too bright. High contrast and sharp edges don't tend to look as pleasing when thrown out of focus.
In your example, the focus point at the left side of the image has some very bright spots in the background, along with some out of focus twigs that IMO are distracting. This is what I referred to about high contrast and sharp edges. Leaves and things look nice when thrown out of focus, the twigs do not.
I think you'll find if you reframe so that your twig only has some nice green foilage in the background, it would look fantastic.