It is really important to breath properly with your diaphragm when you sing.
If you don't, your voice will get tired quickly and feel sore.
I really like the exercise here below, why don't you give them a try!
Hissing
- Breathe in through your nose to the count of 4, breathe out, hissing, to the count of 4
- Then, breathe in for 6, and hiss out for 10
- in for 6, out for 12
- in for 2, out for 12
- in for 4, out for 16
- in for 2, out for 16
- in for 4, out for 20
- in for 1, out for 20
The aim of the exercise is to have an even stream of air and an smooth even sound.
Be gentle when you do the exercise, you should never push or strain.
Practice regularly and you will notice an increase in capacity and an improved technique.
Have fun!