Developing a strong vocal technique involves consistent vocal training over the period of about two years. This assumes that the person takes at least one voice lesson a week. Of course this process can be accelerated by taking more frequent lessons. However one should be careful not to overwork the voice. This would only lead to vocal problems.
Within the vocal technique terminology there are often many terms that are used either interchangeable or incorrectly. For example the word 'chest voice': what does that mean? So it is very important to know exactly what a singer means when they say something, in order to determine what it means to them. It is dangerous to just assume one thing when they mean another. Many times the same term means different things to different singers. Singing is experiential and therefore a singer will associate a term with a feeling. This is the reason that singing is one of the hardest instruments to teach. You can't see it, you can't touch it, but you can feel it. Sometimes there is confusion around vocal technique for a singer. Some of the finest singers of our time will define terms differently.
A vocal-technique is developed through vocal exercises. It is very complex and developing a good technique takes time and careful practice. Good posture and breathing technique are the foundations of a strong vocal technique. But it does not stop there. Vocal exercises are the best way to develop vocal technique. Each vocal exercise may focus on one aspect of singing, however all aspects of singing are inextricably interrelated. One vocal exercise can focus on one or more of the following: phonation, flexibility, range, vowel modification, resonance, projection, strength. However it is important not only to do the exercise but to do it in the proper way so that the voice can develop freely. The goal of vocal exercises is to free and develop the voice in all ways, so that the singer can reach his/her full innate vocal potential.
For the musical theatre and popular singer blending the "chest" and "head" voices is a major goal. Vocal exercises will build the bridge between these two placements. The bridge is the transition notes; they are called the passage or "passagio" in Italian. Every voice has the potential to do this, but it is important to listen to the voice and nuture it carefully.
The irony is that singing with a strong vocal technique ultimately feels easy around the vocal mechanism, because everything is coordinating well: the vocal chords are vibrating correctly and the air flow is correct. It seems easy and it truly is once you put the effort into finding the way and consistency into lessons.