Addons that help with a pull
Hardcore addon - tracks the run and warns about PvP flags.
Enemy cast bars (NeatPlates, ThreatPlates) - shows enemy casts so you can interrupt the spell that matters.
Real Mob Health - shows remaining health so you can decide whether to finish or leave.
Questie - shows quest targets and reduces time spent searching hostile camps.
Other useful tools
Vendor Price - shows vendor value before a full bag displaces a consumable.
Atlas / AtlasLoot - shows dungeon layouts and rewards before the group enters.
OmniCC - puts cooldown numbers on buttons.
Optional damage meters
Damage meters and parse tools can encourage a faster pull pace. Keep the focus on the room, the patrols, and the reset call.
Use the information
Enemy health and cast bars answer clear questions during a pull. Use the information before committing to the next spell.