There are many good spearman builds possible. A safe bet is a balanced 18/18 build but i bet 15/21 or 21/15 builds also work fine.
I'd do something like this:
Level 30
* Strength: 18
* Agility: 18
* Hit points: 63
* Converted: 2
* Ironflesh: 5
* Power Strike: 6
* Shield: 6
* Athletics: 6
* Weapon Master: 6
* Polearm: 156
That's a really safe and solid build. Nice and fast, lotsa hitpoints, good shield skill, enough powerstrike.
Here's the other obvious builds:
Level 30 (4 420 577 xp)
* Strength: 21
* Agility: 15
* Hit points: 70
* Converted: 2
* Ironflesh: 7
* Power Strike: 7
* Shield: 5
* Athletics: 5
* Riding: 0
* Horse Archery: 0
* Power Draw: 0
* Power Throw: 0
* Weapon Master: 5
* One Handed: 1
* Two Handed: 1
* Polearm: 148
* Archery: 1
* Crossbow: 1
* Throwing: 1
Level 30 (4 420 577 xp)
* Strength: 15
* Agility: 21
* Hit points: 56
* Converted: 2
* Ironflesh: 3
* Power Strike: 5
* Shield: 7
* Athletics: 7
* Riding: 0
* Horse Archery: 0
* Power Draw: 0
* Power Throw: 0
* Weapon Master: 7
* One Handed: 1
* Two Handed: 1
* Polearm: 164
* Archery: 1
* Crossbow: 1
* Throwing: 1
You could also try different a spearman / thrower hybrid. You could even go cav if you want with those builds. Not much you can do wrong, everything has it's advantages.
Decide wether you want to be able to move fast or hit hard. Move fast? High agi and athletics. Hit hard? More powerstrike. Pick something that suits your personal style.
As a spearman, you often play a support role in the mob. Stay near other players and use that fantastic warspear to quickly jab at players as they try to swing at your teammates or otherwise expose themselves. Warspear and Battlefork are both great, i believe Warspear is the weapon of choice for most spearmen.
A pike is also great, if you dare going shieldless from time to time. Practice the spinthrust, so you don't glance the point blank stabs.
One problem i encouter when trying to go spearmen: really fast attackers tend to facehug and spam you, making it hard to get a stab in. So in duels, the spear + shield doesn't work very well. If you are good enough, consider put that shield on your back and manual block in a duel type fight, so you have more swing directions to throw at your enemies.
Also, i've seen people walk around with shorter spears and a shield. A secondary polearm for close combat might be useful.