To level up fast in The Elder Scrolls IV: Oblivion, here are the most effective strategies:

Power Leveling Major Skills

• Choose Athletics or Acrobatics as a Major Skill and continuously run or jump to quickly increase these skills. For example, swimming in one direction or jumping nonstop will rapidly raise these skills and trigger level-ups

• Block is another good Major Skill for fighters, as fighting naturally increases it.
• Other easily leveled skills include Light/Heavy Armor, Sneak, Mercantile, and Speechcraft

Efficient Leveling for Maximum Attribute Gains

• To maximize attribute increases (up to +5 per attribute at level-up), raise at least 10 points combined in the skills governing that attribute before leveling up.
• Avoid choosing all three skills of one attribute as Major Skills to prevent slow leveling.
• Plan your skill increases to get 10 skill-ups in three different attributes per level to gain +5 in each attribute

Magic Skills Fast Leveling

• For magic skills, create high magicka cost custom spells and spam cast them to level skills quickly.
• Use the Spell Making Altar at Frostcrag Spire and craft powerful spells for Destruction, Restoration, Conjuration, Illusion, Mysticism, and Alteration

• Alchemy can be leveled by crafting potions like Restore Fatigue and selling them to fund spell-making supplies

Practical Tips

• Use places with low ceilings to spam jump for Acrobatics leveling.
• When stamina is depleted, wait an hour in-game to restore fatigue and continue.
• Rotate between different skills and gameplay mechanics to level diverse skills and attributes efficiently

By combining continuous skill use in Athletics/Acrobatics, strategic attribute-focused leveling, and efficient magic skill training, you can level up very fast and build a powerful character in Oblivion