Your main skills with be based around the AoE/prot spec paladin, but you can play a mage as arcane/fire or frost.
The paladin is relatively low maintenance for holding aggro - Always have Righteous Fury and a Shield Spike on.
Open with Avenger's Shield or standard melee attack. Use Consecrate to build aggro with Blessing of Sanctuary, and keep Seal of Light up to maintain health since you don't have a healer. Keep Holy Shield up for more aggro and damage reduction.
That's all you really need on the paladin's side.
For the mage, you can either go with Arcane Explosion, Flamestrike, or Blizzard/Frost Nova/Cone of Cold to mass-DPS the group stuck on the paladin. Arcane Explosion is the easiest since you don't have to worry about targeting.. but Cone of Cold also works since the mage will probably be following behind the paladin. It just depends on what style of mage you want. Frost is a little more work, but that's what I enjoyed.
Here's a sample setup:
shift-1 - paladin avenger's shield
shift-2 - paladin /startattack, empty on mage.
shift-3 - paladin consecrate
shift-4 - paladin's holy shield
shift-5 - paladin's seal of light
shift-6 - paladin's judgement
alt-1 - paladin's righteous fury
alt-2 - paladin's blessing of sanctuary
alt-3 - paladin's blessing of salvation
alt-4 - paladin's blessing of wisdom
1 - mage's /follow <paladin>, /target <paladin>target macro; empty on paladin
2 - mage's /target <paladin>target, /cast Arcane Missiles (or Frost Bolt, or Fireball); paladin's holy shield
3 - mage's /cast arcane explosion; paladin's holy shield
4 - mage's /cast arcane blast (or Fireblast, or Ice Lance); paladin's holy shield
5 - mage's /cast cone of cold (or Pyroblast)
6 - mage's /cast flamestrike (or Blizzard)
You can remove the paladin's holy shield from 2 to 4 keys to conserve mana, but it's great to have that spammed at later levels to hold aggro & reduce damage.
Those keys will do almost everything you need for most mass-pull situations. Add in water/food/CC/heals to other keys.