Spam your enmity AoE 4-5 times on trash pulls, use your enmity combo 2-3 times on bosses, and use damage-reduction cooldowns on tankbusters (you'll learn what each boss's tankbuster is fast, even if you get hit with it once while learning). This will give you way more enmity than you'll need, but if you do this you never have to worry about losing aggro even if you don't use a single enmity skill for the rest of the fight, and you can reduce your enmity-building skills once you're used to tanking.