What you do kind of depends on the amount of mobs, and what it is your fighting, and what your groups goal in mind is because you'll have to change your strat depending on the scenario, but the best thing you can do is always utilize your Cooldown moves like Spirits and Circle of Scorn and Rampart while your GCD is active, it helps minimize downtime when your not building hate and allows for more consistent threat building.

Your bread and butter rotation on a mob will usually consist of

Fast Blade > Spirits Within on GCD (If Ready) > Savage Blade > Circle of Scorn on GCD (If Ready) > Rage of Halone

But this can vary like I said. To give you an idea of different, here's how I typically pull in different scenarios.

Single Target Boss: Flash > Fight or Flight on GCD > Fast Blade > Spirits Within > Savage Blade > Circle of Scorn > Rage of Halone

3 or Less Mobs Close Together: Flash > Fight or Flight > Flash > Circle of Scorn > Fast Blade > Spirits Within > Savage Blade > Some Cooldown if needed > Rage of Halone > *Swap Target > Fast > Savage > Swap Target > Rage of Halone > Return to *

If they're close enough to link but far enough apart where Flash won't hit them all initially, use Shield Lob to get the mobs to converge on you. You may have also noticed I put Circle of Scorn before Spirits within this time, this is because the DoT from CoS will help maintain hate easier on off mobs when you have AoE DoT centric jobs like Bard and SMN.

4 or More Mobs: Flash > Fight or Flight > Flash > Circle of Scorn > Flash > Spirits Within > Flash > Fast Blade > Savage Blade > Rage of Halone > Flash > *Swap Target > Fast > Savage > Swap Target > Rage of Halone > Flash > Return to *

Any Real AoE Zerg Scenario: Flash > Fight or Flight > Flash > Circle of Scorn > Flash > Spirits Within > Flash Till out of MP > * Target Highest HP mob > Fast Blade > Riot Blade > Flash > Return to *

Maintain that rotation until the mobs numbers get burned down to a sparse few, then either work on regaining your MP with a Fast/Riot Combo or kill them off.

Another thing to keep in mind is, even if your not spamming Flash for lots of mobs, be sure to utilize Flash regularly if a mob can be blinded. You'd be surprised how often you can dodge attacks despite having the evasion of a brick wall. I personally recommend using Flash after every 2 or so Rage of Halone combos and use your defensive buffs when flash's effect has worn off, this gives both your defensive buffs and the resistance timer a chance to cooldown/expire and gives you more overall mitigation long term.