Any half-decent theatre company will have a system for for helping all aspects of voice training.
When MacColl set up The Critics Group he produced a regimé of exercises which had been part of his work in Theatre Workshop. These were for improving pitch, tone, range, relaxation, breathing, projection, vocal dexterity, articulation etc - all essential elements of singing.
They took a short time to learn, but once you had them, they never left you. Then, as he often said, you could get on with the real point of of singing, "enjoying the song".
Jim Carroll