The most important thing to remember as a Reaver is that undead are your enemy of choice. All undead take extra damage from Spirit-based spells, which means your debuffs will debuff more, your Lifetaps will do more damage and more healing, and your DoT and Wrack will do more damage.

Flexible Reavers should always carry two weapons: A Crushing Flexible weapon, and a Slashing Flexible weapon. Different monsters are weak to different types of damage. Skeletal undead are weak to crushing damage, while zombie types are weak to slashing; ghosts and spirits are, unfortunately, resistant to all types of melee damage.

Most people these days have a very simple answer for where to hunt: Task dungeons. Task dungeons are predictable, mindless, unchallenging - they're the very definition of a grind. They also offer substantial experience rewards when completed.