Hi there
Agree with pretty much most of the above, but what I will say as being a Vocal Coach myself, is that far to much emphasis is put on the breathing aspect of the training. The key elements of the "art" is knowing how to use your instrument to it's fullest and with ease. Once you learn how to use the correct muscles and in the right way, the less the others will over compensate and hamper your performance.
Once this "ease" is achieved then the necessity to be breathing correctly is less important.
I can stand on my head and still climb nearly 5 octaves without breaking a sweat... no posture there ;-)
One thing that nobody has mentioned and is probably THE most common issue with a lot of vocal issues is tension. Whether it be in the tongue, in the throat, or in the neck - these are all contributory factors.
There are so many exercises for different disciplines that it would take far too long to go through them all, but suffice to say that for every issue there is a solution (presuming you don't have a medical problem of course).
Without hearing and seeing you it is impossible to tell what you are doing wrong and therefore how to correct it.
I get many singers who complain that after a run of 3 gigs their voice is weak and tired and croaky and they blame the clubs, the weather etc etc when in reality it's the weakness of their muscles and the fact that although they sound good they're not singing correctly.
I am using myself as an example because I was one of them - I was one that had to belt out songs and concentrate 100% on every note every song and felt exhausted by the end of it - Michael Bublé songs are quite challenging - however, after studying for the past few years I now have a comfortable 5 octave range in FULL voice (no crack) - I sing daily for 4/5 hours and wake up bright and breezy around 8am and before I've swung round to the edge of the bed I can "la" up through the registers to almost high C .... I couldn't have dreamed of doing this 3 years ago!
That is not even scratching the surface of course, it's a VERY complex subject and one that requires discipline and passion to get the best results.
Just two things that I wanted to mention simply to dispel any myths out there:
1) If you don't have vibrato - you can learn how to develop it - if you have vibrato but it's too slow or too fast - you can learn how to change the speed of it, if you have a nice 6 osc vibrato but it's constant then you can learn how to control it and bring it in and out whenever you wish
2) If you are "tone deaf" - you won't be for long. Most people I've coached have learned to sing on pitch after just 3 sessions. With a bit of concentration and hard work it can be achieved, despite many saying you have "no hope"
3) Go for your dreams... one of mine was to be able to sing Earth Wind & Fire's - Reasons, with the epic high notes by Phillip Bailey... it's an EASY song to sing now, in the right key and yes, I can do the high notes and whistles ;-)
Even if you're a good singer, you can develop and learn skills to make you a GREAT singer.... the only thing that will stop that from happening is you
Hope that helps some way into understanding a bit more.
Tony.