I've tried many times to do battlebacks, it's really tough.
Perspective and layering are two key bits of advice I can give from what I've learned.
Perspective, try to keep this consistent, grab yourself a perspective template and use that as a base for all your backgrounds. When combined with layering you'll be able to create many combinations which will really help create a collection of assets which will in tern be useful for people as it then gives them choice.
Layering, much like the default two options within RPG Maker but I found that having your own layers when creating backgrounds helps. Foreground with not much clutter and would usually be obscured by user information (such as actor information boxes and command menus). Main ground where the actors and enemies would stand, and free from any obstacles that could potentially look out of place if a actor/enemy crossed or stood upon. Also with this section keeping to proportions helps.
Finally the background, like you've created there a nice example of the surroundings, Landscape details and key focus points.
I do like your work there. I personally prefer a central vanishing point to help with entities being on either side or facing towards the player. Also the high wall near the foreground could cause a layering issue as one of the things I mentioned earlier.
EDIT: Threw some battlers in there and your colours are perfect and with the low saturations makes a perfect background. You'll see the enemies foot layers over the wall where that looks odd. Enemies run in from the left so with that there it'd be above it and would look odd. The vines that go above the wall look floating upwards, if they're on the ground then have them go with your perspective.
Overall it's a great job and I hope this helps that little bit more.
