What do you think can improve the coherence of a qubit? Can you think of what decoheres a qubit?
Heat for example can decohere a qubit, as it gives thermal energy to the system. Unwanted magnetic and electric fields introduce decoherence in the system as well. These fields can drive quantum states, meaning that they couple with the environment.
Another source of this phenomena is crosstalk: when qubits introduce errors to each other.