I know it takes practice. How do you get power when coming in
on a chorus section of a song. Any other part of a song is not a
challenge at all for me usually it seems when I need power for
powerful parts or expression of song.
A good breathing excercise is to lay down and put a book on your tummy. It should rise and fall as you breathe and your shoulders should stay still. It's how most people breathe to sleep. Now the trick is doing it standing up. Controlling an exhale takes practice but remember to drop that jaw when you can, speak all your words clearly and don't try to sing or you'll lift your voice into your head voice and it will sound bad. For control try to aim your voice at a wall and don't let it waver. It's all in the practice so make sure you do scales and singing everyday and keep that throat lubricated with lots of water. Good luck.
I might just add that if you don't have power or feeling in your voice you're probably singing from the wrong place and breathing wrong. It's like talking with style. You can yell at someone right or express yourself talking? Then you can sing, you just need to learn where to sing from and then practice.