If you want to win you got to harass. You can't just wait till you hit max population then attack because any good player would have already killed you by then.
Here are some tips for UNSC:
As UNSC never EVER go air! Only build power turret tanks or gauss hogs.
If you see two covenant players on the other team and they're not both the arbiter go gauss hogs.
If they are both arbiter go PT tanks(Don't research grizzlies their special ability is worse, and they do less damage.).
If you see a prophet on the other team always go gauss because it will make his leader and units useless.
Tips as Covenant:
As soon as you're leader spawns go to the enemy Covenant base,(If there is one.), and start attacking it. Port in some units(Brute Squads/Suicide Grunts) to keep down any warehouses or summits. You should target summits before warehouses if you can.
I would not recommend using the prophet because he is the worst leader in most situations.
Go banshee's and if the enemy covenant player starts to go air transition into vampires.
If there isn't a covenant player on the other team don't send your leader over to their bases and just go banshee's.
