Trample

Trample is Alistar's Innate Passive. After using an ability, for 3 seconds you will deal magic damage in an AoE around you (similar to Sunfire Aegis) to enemies AND structures within the radius. Space out your abilities so that you get all 3 ticks of Trample off when pushing down a tower.

Q - Pulverize

Pulverize is an AoE ability that will knock up all units hit after a very short cast time. This cast time is long enough that fleeing enemies will escape if they are on the edge of the range when activated. After using this skill, walk in front of them and Headbutt them backwards.

Max Pulverize second because its cooldown is much higher than Headbutt.

W - Headbutt

Headbutt is a targeted short range dash that can be used on enemy champions, minions, and jungle monsters. After colliding with an enemy, they are knocked away a moderate range. This can move enemies over walls, so be careful not to give your opponents a free escape. Combo this ability with Pulverize to get in range without knocking your opponents away. More info on this combo in the Unique Skills section.

Max Headbutt last.

E - Triumphant Roar

Triumphant Roar is an AoE heal for all friendly champions and minions, healing Alistar for the full amount and half to everyone else. Whenever a nearby enemy unit dies (minion, champion, or jungle monster) the cooldown of this ability is reduced by 2 second.

Max Triumphant Roar first to get a massive self heal and sustain for your lane partner.

R - Unbreakable Will

Unbreakable Will is Alistar's Ultimate Ability. Upon activation, Alistar will break free from all disables and gain a massive AD boost and damage reduction. You should use this ability when committing to a kill, starting a teamfight, or to push down a tower fast that's undefended.

Flash

Flash is a pretty standard Summoner Spell. You can use it to engage, escape, or to block a skill to save your ally. I suggest taking this 100% of the time on Alistar.

Ignite

AD Carries by default take Barrier nowadays, so picking Ignite will mean being able to make sure your lane partner will get at least an assist if they just don't have enough DPS to pick up the kill.

Exhaust

Exhaust is good to take when your enemy team has a heavy AD carry that's hard to shut down if they get ahead, such as Tryndamere, Kha'Zix or Vayne. You can also take it if you feel your ADC got counter-picked or has just a weak matchup.

Teleport

Teleport can be used to save your teammates in other lanes, or to defend an exposed tower. Alistar performs especially well with it. Teleport behind an enemy and simply Headbutt them into your team.