I prefer a natural looking tank.
Dark or muted mixed colors of substrate, like soft grey, tan, brown, black. The fish are supposed to be the most colorful thing in the tank. Plants are supposed to show up against a background. A bright substrate jumps out at you. A dark substrate retreats so the fish show up better.
Natural decor like rock, pebbles, driftwood. No glued-together towers of rock, no 'Roman ruins'.
If you like these things, OK, go for it.
More plants. Better distribution of plants.
Move the larger plant to right behind the 'Roman ruins' to balance the tower of pebbles.
Create a large uniform area by planting several of one species of the smaller plants.
Bring the bridge up front, and make a bit of a scene with different substrate, and different heights of substrate. A bridge is for crossing a stream, or a low spot between 2 hills. So make at least a couple of hills with a stream, or low area, and use the bridge to cross that. If you sorted out all the gravel then the brown becomes the basic soil areas, the blue becomes the deep, shaded parts of the stream and white becomes the faster moving parts of the stream between the hills, or the white might be used like snow on the peaks of the hills, or used to frame the picture by making a line in front.
I would take the gravel out and put in a darker color or get sand. Now if your going to do sand do not get the play sand that is really fine because that stuff just looks really fake when trying to make a natural looking aquarium if that's what your going for. The sand I hear a lot of people use if there not buying like ada sand, is the pool filter sand. Also I would try and find a nice peace of driftwood. Small plants in front medium plants in middle and taller plants in back. If using gravel try and slope it if it's possible to do without it just flattening out. I know it's eater said then done but I hope I could help give you a small chunk of my knowledge of what I have seen works best! Good luck!