Singing is a form of athletics. You need to be in good aerobic shape.
Fast walking, swimming or any activity that stimulates the intercostal muscles
and permits relaxed breathing is desirable. Stay away from alcohol as it dries up the vocal cords. Smoking will cut down on your wind.

Singing louder is about a balanced focussed singing, not necessarily volume.
Sometimes the louder you push, the less it carries.

A good voice teacher is worth everything and can show you how to project without belting or straining.