Keep working on it!
For a first map, it could be a hell of alot worse - but it seems like you’ve picked up a few basics, you can arrange and texture brushes and have some knowledge of entities. Practise, practise and practise. Make more maps like this but don’t release them, you’ll pick up knowledge on the way.
In this case, ways to improve this map:
There’s an entity called light_environment which is intended to simulate actual light instead of illuminating everything in the map as is currently occuring. Place one of them somewhere up in the sky.
The textures on the ground need a bit of work, as it repeats horribly and looks unnatural. Try using different textures and blending. There are plenty of tutorials on this.
The ground is very blocky. Try learning to use displacements to create rugged, more natural looking land. Again, there are plenty of tutorials on how to do this.
But primarily, as I mentioned before, don’t worry about releasing anything. Just keep practising, learning and having fun. After a while you’ll find that the largest problem you’ll encounter is optimization and diagnosing errors but you’ll get a good idea of what looks good and works well.