What you need to make those ferns "bushy"

D) is time.
That's it.
They aren't particularly fast growing, but if the conditions are right they will grow faster.
Your Java fern looks very healthy, all you need to do it cut off any old leaves that look like they are covered in algae (if you get any).
Though they can do great in low light, if you want them t look "bushy", put them in the brightest position and give them lots of area to cover.
In my main tank, I started off with putting Java fern in the shaded areas. Over a few months they grew very bushy, and started shading some of their own leaves. Those leaves got algae on them and I'm too lazy to prune in that (2' deep) tank so they eventually fell off.
One of the leaves that fell off naturally got trapped on a bit of wood higher up, and within a few weeks it quickly became bushy and green in the area of high water flow and light.
When the powerheads intake gets clogged with dead leaves though, the older leaves begin to get covered with algae, and it looked like this (taken this minute):
Bushy, but not bright green looking. This is Windelov Java fern though, it's more prone to this.
All I need to do do to make it look nice again is clean the powerhead and cut off the algae covered leaves.
The regular Java fern in my high-tech tank is in a low light area, but has no visible algae on it due to the flow.
All you need to do is place the fern in an area of high light and flow, and it will look excellent.