Life: Life related powers would be kind of like healing, but on a larger scale. You can't bring back the dead, but you can create beings, plants, anything considered as a 'living thing' is up to you. If something is sick or dying, you can breathe Life back into them. You balance the scales, helping the good survive and letting the evil go. Or maybe you'll mix it up.
Death: You can kill humans, but you need to be exact. Was it a heart attack? A stroke? Allergies? When someone is dying, you take their soul, sorta like a grim reaper. When you do, you gain more power. As Death, maybe moderation is good. But I never set down guidelines like that, it's up to you if you'll be good or bad.
Fire: A weapon of mass destruction and devastation, yet beautiful and bringing hope and light. Similar to Death, it's up to you if you want to be good or bad. Maybe you'll save a lost person, helping them start a fire to stay warm and use smoke signals (idk that was random) or maybe they'll cause a wildfire and burn down forests.
Water: Humans, plants, and animals all need water to live. Even in the dry desert, you bring mercy to every cacti and every creature with rainfall. Even though you can kill millions with a tsunami, you are a sustaining force of Life and crucial to existence, I think I speak for humanity when I say "I hope Mother Earth picked this one well."
Air: "Oxygen, wind, tornadoes and breezes. You clean the Air and purify it of pollution. You bring breezes that quell the hottest summer days and you devastate when you destroy homes with hurricanes. You can calm windstorms, but who's to say you can't start 'em.
Earth: Plants, minerals, the very ground we walk on. You keep it fertile and clean and bless the humans and animals with crops and good harvest. Or you deny them food and kill the seeds they farm. You also know where every gold mine, every diamond mine, every mine is, and maybe even more undiscovered metals that you hide from the humans, the miners, and keep to yourself. You can cause the ground to tremble or you can bless it. You might open sinkholes and chasms or you might close a few, it's up to you.
Note:
I was thinking, maybe the humans don't pray to any Gods or anything, they pray to the Elements. There might be groups of people who prefer one element above the others. Oh yeah, and before I forget, even if you're "opposites" you don't have to fight. Maybe you work together? During a war, maybe Life and Death co-operate and try to end it as quick as possible. Or maybe go rogue and cause a genocide? We're going to be forming this world.
pEoPLe cOunT oN yOu