How does Bohr improve Rutherford's atomic model?
Rutherford described the atom as consisting of a tiny positive mass surrounded by a cloud of negative electrons. Bohr thought that electrons orbited the nucleus in quantised orbits.
Bohr built upon Rutherford's model of the atom. In Rutherford's model most of the atom's mass is concentrated into the centre (what we now call the nucleus) and electrons surround the positive mass in something like a cloud.
Bohr's most significant contribution was the quantisation of the model. He believed that electrons moved around the nucleus in circular orbits with quantised potential and kinetic energies. So it was not possible for electrons to occupy just any energy level.
In principle the quantisation aspect of the model is still believed to be correct. The main problem lies in the idea of electrons in circular orbits. This does not satisfy the Heisenberg uncertainty principle, which is that it is not possible to know the position and momentum of a particle simultaneously.
For further reading you might want to find out more about what scientists currently believe about atomic structure: https://socratic.org/questions/how-does-the-bohr-model-of-an-atom-differ-from-the-modern-theory