I noticed a lot of only one color of green. . . you could try adding one or two small/medium plants of a different color or shade. That often gives the illusion on more content but simply having multiple shades of a color. . . Or maybe in the back right corner way in the back a medium/large rock of a sandy color, or some small rocks. It seems to be the most bare back there. . .
I like the hill and wood with the moss on it. The assorted rocks in the left front corner aren't doing anything for me. Either get another larger rock and arrange them right on the right hand third mark of the tank, put them so they extend the line of the wood to the right or take them out.
I like the java fern and moss work and the bright green plant under the largest bit of wood [more moss?]. The stems need to be planted a bit apart but in a group and you do need a medium sized rosette plant like a small sword or crypt. Tanks with mostly stem plants are not easy to manage. The Marsilea could be split up more so it looks dotty instead of spotty but it should start spreading the way it is now. Don't disturb it if it is doing fine!
If you put the Cabomba [stems right in front of your filter] on top of the hill it should grow to the surface and drape nicely, cut stems growing too long and replant on the hill. Plant the other stems in looser bunches along the back - not a row, keep in a bush. Get a big pot of an easy crypt like wendtii and split it up into 2-4 bunches and plant in the middle of the tank keeping the Marsilea in front. It will melt into goo but will start regrowing inside a week. I like the line you have going, keep the larger crypts to the left and have the Marsilea wrap around the side of the tank a little bit.