Arena events usually revolve around achieving certain numbers of wins, many times up to 500 or more. Recent changes have seen the goal numbers lowered, but we can't say for certain that it is going to be a permanent change.
Typically, the rewards from an arena event will be talismans, frontier coins, iron coins, souls, soul fragments, gold, skill shards, evo materials, ironite or even sands of war to keep you going.
As with any event, planning ahead is crucial. These will many times follow a sacrifice event, so save up the sands of war that you win from the sacrifices so you're ready to jump in and start attacking.
Many players will advocate for a "Single Ed" defense during these events. This is simply setting your defense team as an Eddie with no supporting characters to make it quicker to accumulate wins and helps keep your ranking down. This essentially means you're giving up any wins on defense in exchange for hoping to run into similar teams or just lower ranked teams when you're attacking / revenging.
Speaking of revenge, keep in mind that you are limited to 20 revenge matches per day and 2x per player, so that list will dry up much quicker than your attack list.
While many players do feel it's good sportsmanship to run that style of defense during these events, always remember it is your game to play and nobody can tell you how to play it.