The easiest skill to get to 100 by far, is the Alteration skill. First, you'll want the Telekinesis spell, which you can get from the following locations:
(From the wiki)
May be purchased from Tolfdir at the College of Winterhold. (Requirement: Level 40 Alteration)
May be purchased from Wylandriah at Mistveil Keep. (Requirement: Level 40 Alteration)
May be found in Labyrinthian. (Requirement: level 50 Alteration)
Found in a cell in Redwater Den near a dead character.
Can rarely be found in the Master locked chest in the Thieves Guild.
Found in the first room of Benkongerike's Great Hall, it is hidden beneath a pile of Lusty Argonian Maid books.
May be found in the safe of Proudspire Manor.
May be found in the chest close to Word Wall of Autumnwatch Tower.
May be found in a chest in Uttering Hills Cave.
May be found on a Seeker in Apocrypha.
May be found in Dwarven chests.
May be found in Giant Camps.
May be found in chests at Dragon Lairs.
After that, you'll need to reduce the spell cost to 0. Through a mixture of either purchasing the Adept Alteration perk or finding/making enchanted equipment that lowers the cost of Alteration spells. Finally, go to any place you can fast travel from, drop an item and use the spell on it. While you are using the spell on the item, fast travel to another place on the map. When you arrive the skill will instantly be a 100, making for an easy way to level up as well.