The first is that singing effectively doesn't always mean singing louder. You may see this in amateurs, that they push their voice and raise the pitch thinking this is going to project the singing or make it sound better. The sound instead just becomes screechy and pitchy. When learning to effectively sing you need to sing from your entire body; the back muscles, the diaphragm, and the entire voice box are involved. Control is the key; you need to control your voice, the pitch, and the tone in order for it to sound better. This means not just singing "more" but controlling the vibrations that begin in the throat for a deeper, richer sound.
How to Start Singing