AT Temple (in the 70s) I studied diction and phrasing in a voice training course. I was a woodwind major, and playing the clarinet was by far, the best thing I could have done to develop good breathing habits.
The diction part was important, but more than that is something that I have stated many times here:

LEARN THE WORDS.

You can't fully deliver a tune if your eyes are glued to a chart. You need to understand what the lyric means before you can transfer those words into an emotion that will touch the listener.
Many great singers, dont have great voices.
It's all in the presentation and the honesty of the delivery. Listen to Jimmy Durante or Sachmo sing a love song ..... it's beautiful, moving and inspiring on ANY level.
Take a finely trained voice, and subtract the emotion and you'll get "Ho Hum".

Guys like Jim Nabors and Andy Griffith have beautiful natural voices, but I can't get into the phrasing and delivery that they use. It's the tool INSIDE your head that you can reach people with. The mechanics are the easiest part to master.

Of course, if you have NO ear for pitch and bad timimg .... you're going to need to be VERY charming to sell the tune !

Record your self as much as possible ..... it really DOES help to show you the correct path. You can learn alot from a recording. (sometimes, a hard pill to swallow!)

Good luck, and don't aim for a "B" ..... shoot for the stars, and you'll get the best you can from the effort.