Always try to bring an ally with you. Both players will receive Ally Tickets which are used to open a specific kind of chest with various rewards. You can send a friend request after the level is over; you will get better rewards if you play with the same partners multiple times.
Elements
There are five elements. Each weapon and monster has a specific elemental affinity. Fire is stronger than Nature, Nature is stronger than Death, Death is stronger than Light, Light is stronger than Water, and Water is stronger than Fire. When selecting a level, the difficulty section will reveal what type of enemies you will be facing. Before starting, select gear that will give you an advantage. Use enemy weaknesses to do higher damage.
Fusion
Fuse unneeded equipment with same elemental property as gear you want to upgrade. Save equipment that has the same element as your favorite gear to sacrifice as material to fuse.
Traps
Traps will begin appearing at level 4. These include explosive mines on the ground, spring-loaded spike trips, and other devices. If you trigger a traps, quickly use dodge roll. Because you are invincible during a dodge roll, with proper timing you should avoid damage from the trap. This can also be used during Boss attacks.
Weapons
There are five different weapon classes. Great swords swing slow but do a great deal of damager per hit. Dual blades are less powerful, but are very quick and allow you to attack multiple times. Glaives are long spears that have good attack power and long reach. They are useful when taking out groups of enemies. Staves are magical rods that have elemental properties that allow you to cast long ranged magical attacks. Crossbows are ranged weapons that are less powerful but allows you to take down enemies at a distance.