How lovlely to have a new tank to play around with!
I do agree with the privious post that consistancy i key in creating an over all pleasant look. However, inconsistancy is a good tool to put focus on whatever is conistant!
The substrate you've chosen has alot of details and the rocks are inconsistant in colour, so from my point of view you need to decide on a focus point
The red stone is a bit out of place but I think the rest are fine. One way to sew it all together could be to use alot of the same type of plants who has that consistant feeling. Anubias comes in alot of shapes, but all look quite alike and can be placed both in the substrate and on top of things.
As for the hardscape, I think the root sticking up to the right creates sort of a barrier, making the far right of the tank a dead area viewing-vise. One way of doing it is to put the part sticking up amongst the rocks to the left, and placing the twigg to the far left in the back corner. It would create a feeling of space, as the barriers are to the left and then the tank opens up
This is just one out of an infinite ways of scaping your tank!
Whatever you decide to do, try to figure out some feeling you want to achive, like roundness, space, jungle etc, and then think about what is needed to create that feeling, what plants are needed and where to plant them etc. Look at pro-scapes and look beyong the beauty to focus on what could be the reason they are precieved as beautiful.