Using Pulverize can allow Alistar to establish better positioning for Headbutt.

Using Flash to get behing an enemy and Headbutt them into your tower early game can devastate them and get an early first blood.

Using Flash can allow you catch his target off guard to knock them back into your allies with Pulverize and Headbutt.

Using Pulverize immediately after a successful Headbutt will apply the stun from Pulverize. Instead of being pushed back, the target will be knocked up and stay in place. This can be useful in some chase situations (make sure you succeed or you will knock them further away).

Hitting an enemy into a close-by thick wall with Headbutt will stun them for 1sec. Reason being that they will still try to travel the distance even if a wall is in the way. However, if Headbutt is used near a wall, it sometimes sends the enemy onto the other side which allows them to escape. This can also be used to your advantage. Sending the enemy tank or a high damage dealing carry (like Fiddlesticks after he uses Crowstorm ) over a wall can allow your team to win a 5v4 match.

Most walls in the jungle and river are thin, but whether they will go over them or not depends on how close they were to the wall when you headbutted them.

Unbreakable Will should mostly be used when turret diving or in team fights when focused by the enemy team.

Triumphant Roar enables you and your allies to stay in your lane for longer periods of time.

Alistar is ganker due to the fact that all he needs is his Pulverize and Headbutt combo to gank a lane.

You can also consider to buy some items like Quicksilver Sash witch costs only 1,440 and it offers you +56 Magic Resistance, + Active effect: Removes all debuffs from your character.
90 second cooldown. This item works like Cleanse but has 20 sec. less cooldown.

I would also recommend buying Spirit Visage witch costs only 1,550 and it offers you +30 Magic Resistance. +250 Health + UNIQUE Passive effect: Reduces ability cooldowns by 10% and increases your healing and regeneration effects on yourself by 15%.

If you Think that this build does not provide you with enough mana you can also consider buying Frozen Heart witch costs 3,075 and gives you +99 Armor. +500 Mana + UNIQUE Passive effect: Reduces ability cooldowns by 20% and reduces the attack speed of nearby enemies by 20%(this is more AD defence item).

Pulverize- (Active): Alistar smashes the ground where he is standing, dealing magic damage to all enemies in the area and knocking them up for 1 second and stunning them upon landing for 0.5 seconds. Radius of AoE: 365.
Cost: 70 / 85 / 100 / 115 / 130 mana
Cooldown: 17 / 16 / 15 / 14 / 13 seconds
Magic Damage: 60 / 105 / 150 / 195 / 240 (+0.6 per ability power)

Headbutt- (Active): Alistar charges at an enemy, taking its position, and rams them, dealing damage and knocking them back (no stun).
Range: 650.
Knockback Distance: 650.
Cost: 80 / 90 / 100 / 110 / 120 mana
Cooldown: 14 / 13 / 12 / 11 / 10 seconds
Magic Damage: 85 / 130 / 175 / 220 / 265 (+0.8 per ability power)

Triumphant Roar- (Active): Alistar lets out a commanding war cry, instantly restoring health to himself, and healing nearby friendly units for half of that amount. The cooldown is reduced by 2 seconds each time a nearby enemy unit dies.
Cooldown: 12 seconds
Radius of AoE: 200
Cost: 20 / 30 / 40 / 50 / 60 mana
Self Heal: 60 / 90 / 120 / 150 / 180 (+0.4 per ability power)

Unbreakable Will- (Active): Alistar lets out a wild roar, removing all crowd control effects from himself. He also gains bonus physical damage and takes 75% reduced physical and magic damage for a few seconds.
Cost: 150 mana
Cooldown: 120 / 100 / 80 seconds
Duration: 6 / 7 / 8 seconds
Bonus Damage: 60 / 75 / 90

If you are solo laning or if you are unskilled player, you can consider taking E (heal) in the early game to stay longer on the lane.

If you are Jungling you should go in Q (PULVERIZE) and E (Heal) as your 1st skills.

Alistar is one of the best solo laners, he has skills to face up to 2 enemies on one lane straight as the game starts.

In 1 vs 2 laning, Alistar can use his W (HEADBUTT) to push away one of the enemy champions as he focuses at the other one, he also can use W (HEADBUTT) to push away one of the enemy champions and then stun the other one by using Q (PULVERIZE) witch will make the enemy champions Take DMG and leave Alistar with no DMG taken.

In 1 vs 1 laning Alistars combo depends on if the enemy champion is Ranged or Melee.
If the champion is try to attack him/her by using W (HEADBUTT) or if the champion is low on HP I would recommend to flash behind them, push him/her towards your base and stun him/her while he/she run's back.

Always make sure whether your target owns cleanse.

Try to keep in safe while playing.

Its worth to use ultimate to to save yourself.

Whenever you have a chance, try to push your opponent under your turret, best way to do that is by approaching him from the back or flashing behind him followed by W (HEADBUTT) and while the enemy tries to back away from the turret, you come towards him and use Q (PULVERIZE) to stun them.

Always make sure what summoner spells does your enemies have.

Make sure that they don't have lots of stuns or disablers, you also have to watch out at charging champion's abilities like Xin's Audacious Charge or Katarina's Shunpo.

Always go for the Blue buff (Mana Regeneration) if its available.

Always try to go back on a lane with a sight ward and place them on a river in bush/grass places.

U always have to turn your ultimate on then charge first into the team fight by using W (HEADBUTT), in this way U wont loose any valuable time of your ultimate (this is recommended only in a late or sometimes in mid game dependent on how feed you are.

In Early game team fights I would recommend you to use your ultimate and just try to take them out by using W (HEADBUTT) and use stun to get time to run away from danger.

Always remember to turn your ultimate on before you rush into any fight (apply to ganking dependent on the situation) this will decrease DMG taken(by 75%) for a small amount of time.
Always remember to use Q (PULVERIZE) to stun the enemy and prevent her from making DMG.
If you want to keep on fighting and need to use W (HEADBUTT)I would suggest to use it on an enemy champion to push him towards the wall so he cant run away. Otherwise if u want to run away push away the enemy and if it will get too close i would recomend to stun him by using Q (PULVERIZE) and push him away again by using W (HEADBUTT)if the skill is available.

while your team is chasing someone you should flash in front of them, use Q (PULVERIZE) and then W (HEADBUTT) to push them towards your team, after flash you can also use W to push them straight away and Q (PULVERIZE) to stop them from running.

Ultimate On - (1 vs 5)
Annie(900AP) = about 20 dmg from basic skills and 80 dmg from Ultimate.
Xin (400 AD + critics every hit) = Killed himself by attacking me (thorn mail).
More than 95% DMG decreased.

Ultimate Off - (1 vs 3)
I would recommend going up to 1 vs 3 otherwise you can get killed.

I think that Flash and Ignite are the most appropriate summoner spells for this build/guide but you can still experiment on them.

If You Jungle with Alistar you should consider Taking Smite + Flash because Flash is the main summoner spells needed to use in this Guide

If you are Jungling you should maximize your skill points in Q (PULVERIZE) and E (Heal) as your 1st skills/abilities.

Pros

Easy to Play
Good in a team fight
Good solo lane
Good Jungler
Cheap
Easy to kill with in early game
High HP Overall
Heal skill - The cooldown is reduced by 2 seconds each time a nearby enemy unit dies.

Cons

Short stun time
Useless passive in tank build
Weak Heal

Unfortunately alistar's passive has been changed
Before - Alistar deals 50% increased DMG to a turret
Now - Each time Alistar casts a spell he will be able to move through units and will deal 9 + (1 x level) + (+0.1 per ability power) magic damage per second to nearby enemy units and structures for 3 seconds. It deals double damage to minions and monsters.