Pinball:Skills

Each Skill has a specific way to increase its level. At certain levels, there are certain perks that unlock.
Smithing, increased by crafting items. Takes 3 'crafting points' per skill level up. Armor is worth 3 points, two handed weapons are worth 2, and one handed weapons, shields and arrows are worth 1.
Level 1: Iron Smithing
Level 20: Steel Smithing
Level 40: Orcish Smithing
Level 60: Elven Smithing
Level 80: Glass Smithing
Level 100: Dragon Smithing
Armors, increased by being hit by Melee or Arrow attacks while wearing Armor. 3 hits for the first level up, and +1/level after.
Level 20: 10% Melee Resistance If Wearing Armor
Level 30: -50% Stagger If Wearing Armors
Level 40: +10% Melee Resistance If Wearing Armor
Level 50: -50% Stamina Consumption If Wearing Armor
Level 60: +10% Melee Resistance If Wearing Armor
Level 70: Worn Armor Weights Nothing
Level 80: +10% Melee Resistance If Wearing Armor
Level 90: Stamina Regenerates 50% Faster If Wearing Armor
Level 100: 10% Chance to Avoid Melee Damage If Wearing Armor
Block, increased by blocking attacks. 2 blocked attacks for the first level up, and +1/level after.
Level 20: Blocking Is 10% More Effective
Level 30: Blocking Depletes 50% Less Stamina
Level 40: Blocking Is 10% More Effective
Level 50: Able to Do Power Bash
Level 60: Blocking Is 10% More Effective
Level 70: 50% Less Damage from Blocked Magic Attacks
Level 80: Arrows Blocked with Shield Do No Damage
Level 90: Blocking Does 2x Damage
Level 100: 25% Chance to Disarm Enemies When Power Bashing
Melee, increased by striking enemies in melee. 3 hits for the first level up, and +1/level after.
Level 20: Melee Attacks Do 25% More Damage
Level 30: Melee Attacks Cost 25% Less Stamina
Level 40: Power Attacks Do 25% More Damage
Level 50: 10% More Chance to Do Critical Melee Damage
Level 60: Power Attacks Have 20% Chance to Stagger
Level 70: Melee Attacks Do 25% More Damage
Level 80: Melee Attacks Cost 25% Less Stamina
Level 90: Power Attacks Do 25% More Damage
Level 100: 20% Chance to Paralyze the Enemy
Archery, increased by hitting enemies with arrows. 3 hits for the first level up, and +1/level after.
Level 20: Bows Do 10% More Damage
Level 30: Power Attacks Have  +10% Chance to Do Critical Damage
Level 40: Shots to the Block Lane Add Time Till the Next Enemy Attack
Level 50: Bows Do 10% More Damage
Level 60: Recover Twice As Many Arrows From Fallen Foes
Level 70: Arrow Hits Will Stagger All the Smaller Enemies
Level 80: Bows Do 10% More Damage
Level 90: Shots to the Block/Flee Lanes Add Time Till Next Enemy Attack
Level 100: 20% Chance of Paralyzing the Target
Sneaking, increased by landing sneak attacks. 2 sneak attacks for the first level up, and +1/level after.
Level 20: 10% Longer Sneak Timer at the Beginning of Battles
Level 30: 5% More Damage from Sneak Attacks
Level 40: Sneak Attacks with One-Handed Weapons Do 4x Damage
Level 50: 10% Longer Sneak Timer at the Beginning of Battles
Level 60: 5% More Damage from Sneak Attacks
Level 70: Sneak Attacks with Two-Handed Weapons Do 4x Damage
Level 80: 10% Longer Sneak Timer at the Beginning of Battles
Level 90: 5% More Damage from Sneak Attacks
Level 100: Sneak Attacks with Bows Do 3x Damage
Lockpicking, increased by opening a lock or breaking a lockpick. 1 lock opened or lockpick broken for the first level up, and +1/level after.
Level 20: Novice Locks Are Much Easier to Pick
Level 30: Apprentice Locks Are Much Easier to Pick
Level 40: Find More Gold in Chests
Level 50: Adept Locks Are Much Easier to Pick
Level 60: 25% Greater Chance of Finding Items in Chests
Level 70: Expert Locks Are Much Easier to Pick
Level 80: Picking Starts Close to the Opening Position
Level 90: Master Locks Are Much Easier to Pick
Level 100: Lockpicks Won't Break
Magic, increased by casting spells, not counting Healing. 3 spells for the first level up, and +1/level after.
Level 20: Cast Novice Level Spells for Half Magicka. Can Dual Cast Spells
Level 30: Can Cast Apprentice Spells. Attack Spells Do +25%
Level 40: Cast Apprentice Level Spells for Half Magicka. Healing Spells Cure +25%
Level 50: Can Cast Adept Level of Spells. Healing Spells Also Restore Stamina
Level 60: Cast Adept Level Spells for Half Magicka. Attack Spells Do +25%
Level 70: Can Cast Expert Spells. Healing Spells Cure +25%
Level 80: Cast Expert Level of Spells for Half Magicka
Level 90: Unlock All Spells
Level 100: Once a Day Heals 250 Health Automatically to Avoid Death

Note that the amount of skill uses is the same regardless of starting character. A Human Knight with 15 Magic and a Human Mage with 25 both take 3 spell casts to gain their first skill level up, to 16 and 26 respectively.