Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
My Alistar Build. More of a support than a tank. He can also initiate though.
Good combo for initiating is Flash > HeadButt > Pulverize.
Pulverize is probably most often used for Alistar especially for team fights and ganks but there is no reason to max it early since it only adds damage. The real use for pulverize is its AoE Stun.
Lastly, Alistar is great for laning. Use Triumphant Roar to heal both yourself and your minions. Mana Regen. is needed because of this skill.