Regular practice is essential. It is very important to recognise that, as a singer, you are a vocal athlete and that you are training a muscular and mental co-ordination. Each time you sing, you are building a muscular co-ordination that controls the breath and resonance that you want. Your development as a singer requires a controlled repetitive approach (that any good athlete would use) to develop your voice and refine your skills, hence the goal to possess good vocal technique.
A vocal coach can guide you in how to warm-up your voice and how to strengthen your voice through various exercises and repertoire.