Sooner or later, when you're learning a new technique or song you will come to a cross-roads of whether you will do things the "correct" way (and we mean genuinely more effective and useful, not traditional or formal) or the easy way. Now I know that sounds like a setup for me to say you should take the high, lonely path to excellence and always do things the correct way - and I am - but I want you to see the point and issues here. Thousands of excellent musicians do things "the easy way" and it works fine for them. They play with two fingers instead of 4, they do vibrato with their jaw instead of their diaphragm, they only play in 4 keys. Making the choice for the "correct" way is about laying a broader foundation for yourself and maximizing your own personal chances of success. Seen 2 years from now, because you played with 4 fingers you can play this b9 chord with ease, because you used diaphragmatic vibrato you are always in tune, now that you've developed a love for jazz or black gospel you discover you can easily move through the changes because you worked in all keys. In the short term you will frequently need to choose the easy way to get the job done at the moment, but keep your eye on the horizon of what you can be, by making the BEST way natural.
Use long tones in songs to discover resonance and roundness in your voice. Experiment with vowel placement for the perfect tone.