The following mastery setup is a good general setup for any ability power carry or mage in the game. The Tier conditions are not known yet. In this guide i assume that they won't be changed, so summoners have to spend at least 4/8/12/16/20 points unlock Tier 2/3/4/5/6 respectively.

Offense Tree

Tier 1

The following mastery setup is a good general setup for any ability power carry or mage in the game. The Tier conditions are not known yet. In this guide i assume that they won't be changed, so summoners have to spend at least 4/8/12/16/20 points unlock Tier 2/3/4/5/6 respectively.

Offense Tree

Tier 1

• Summoner's Wrath, 1 point: Most carries run ignite or exhaust so improving them is a good idea.
• Mental Force, 4 points: This means +4 ability power. The more AP we have the better.

Tier 2

• Sorcery, 4 points: 4% cooldown reduction. AP carries depend on their abilities, so less cooldown can give advantage.

Tier 3

• Arcane Knowledge, 1 point: +10% magic penetration. This really worth the point in my opinion, because most ability power carries use magic penetration runes.
• Havoc, 2 points: +1% increased damage.
  
  AP carries usually don't use critical strike so this one is better for them.

Tier 4

• Blast, 4 points: 1 ability power per level. Raise AP to increase damage.

Tier 5

• Archmage, 4 points: 5% ability power. This looks really strong and a must for all ability power based carries.

Tier 6

• Executioner, 1 point: +6% damage to targets below 40% health. This is pretty good for all carries. Produces better ganking ability and easier minion last hitting.

This can be the typical AP carry build in my opinion. So far we have spent 21 points. Use the rest on the Utility tree.

Utility Tree

Tier 1

• Summoner's Insight, 1 point: Well i doubt that Flash can be nerfed that much it won't get selected by most carries, because this is the only decent gap closer/escape spell.
• Expanded Mind, 3 points: 12 mana/energy per level. Gives slightly larger pool to use abilities.

Tier 2

• Swiftness, 4 points: 2% movement speed bonus. All champions can make use of this, faster movement can help early ganks.

Or

• Swiftness, 1 point: 0.5% movement speed bonus.
• Meditation, 3 points: +3 mana regen per 5 seconds. If your carry is mana based, then this option can be used.

Tier 3

• Runic Affinity, 1 point: 20% longer buffs duration. Buffs play very important role in the game, so the longer they last the better.

I think this setup is pretty good for ability power carries and will be used by lot of summoners. It gives more ability power, better cooldown reduction, magic penetration. Overall more damage.