First of all, those are some very good looking pieces of wood to start with. Good job on choosing them and placing them as you have. You have created an angle which invites the eye into your aquascape, and they make a good foundation to build upon, so leave them as they are. The very first thing that stands out to me is the bunch of stem plants in front of the right-hand piece of wood, nearly center. This is a tall, thin form that needs to be placed toward the rear of the aquarium; where it is left to right is ok, at least for starting, just move it back behind the wood. The next thing that sticks out is that all of the plants are arranged in a fairly straight horizontal line. This acts your horizon, and flat horizons are boring. That's why good landscape photos or paintings never have a flat, unbroken horizon. Think of the underlining "ribbon" beneath the Coca-Cola brand name; that is called the "dynamic wave", and they have it copyrighted because it is both distinctive and appealing. You can use the same line (or similar) in your aquascape design and it will provide a dynamic sense.
Also, all of those stem plants seem to be placed mid-ground, just behind the wood pieces. Since they are so tall, they should be placed toward the very back. Also, trim some of them to different heights, to avoid that boring straight line effect. For just starting out, it's probably best to keep your design simple, so a symmetrical design is good to start with, and that is what you seem to have begun with your foundational wood placement, so make the horizontal top line in back dip down toward the middle and high in the back corners. Generally, you want to place tall forms toward the back of the aquarium and graduate in height as you come forward, with shorter plants in front. One exception to this is that tall or medium-height plants work well in the front corners, framing the scene from the sides.
Now think of yourself standing center stage in a classic theatre, facing the audience. All the seats are arranged in a horseshoe shape around you, and as they go further back, they get higher, with the highest ones in the very back. Also, there are those expensive private box seats high and close to the stage, right? Think of your aquascape as the theatre seats, and your view from the front of the aquarium is like you looking at the audience. Of course, theatre seats are arranged like that so that everyone in the audience can see what's happening on the stage, but it also works in reverse: from center stage, you can see the entire audience (IF the house lights are on, of course). If you follow this simple plan, you will be able to enjoy easily seeing all of your aquascape's features.
Got that? Ok, here's another analogy to help you design your aquascape. Think of viewing a nice, relaxing garden from a bird's eye view. (No, not a vegetable garden! That's work to me, and not relaxing at all!) You want your garden to be a place where you or your guests can wander and relax without having to think about where to go next, and where there is something interesting every now and then along the path, so that you are unconsciously drifting from one spot to the next, never running into a dead that causes you to realize you've been so relaxed that you don't remember getting there. No, you don't want dead ends because you want to be continuously wandering and relaxing. Alright, you get the idea, right? Now apply that principle to the path your eye follows as you look at your aquascape. You already have the two pieces of wood arranged so that they draw your eye from the front of the aquarium toward the middle and back, right? See how that works? Now, if you have already placed that tall stem plant bunch in the back, then that's probably where your eye is led, so now all you need to do is create your visual pathways from there. A good design will invite your eye from one point to another, letting it rest momentarily on certain focal points of interest along the way.
What I've gone over here is just basic design and general guidelines. Once you've grasped these concepts and practices well, then you'll be ready to move on to more complicated designs, ones that are not necessarily symmetrical, yet create balance without having similar objects on each side.
One more thing: you mentioned the Java fern; well they are usually focal points, since they have such large and interesting leaves, and as such can be placed in the mid-ground or to the side, in front (the corners), despite the fact that they may be as tall as many of the background plants. This type of feature usually doesn't block much of the view of what is behind it, so make use of it sparingly until the plant becomes too large and dominant.
I hope this helps you get started with aquascaping your aquarium to your satisfaction, and provides a foundation for you to build your own skills upon. Good luck, and enjoy the process!
"May the Fish be with you."