How do you rank up in Battlefield 3 multiplayer

In Battlefield 3 online multiplayer, the player can rank up by gaining points. There are many, many ways to gain points. Not all ways to gain points yield the same amount of points. Some ways to get points include:

• Killing enemy players (100)
• Damaging enemy players and a teammate finishes them off (10-100)
• Disabling enemy vehicles (100) and destroying enemy vehicles (50)
• Capaturing a flag (250, Conquest)
• Assist capture (50)
• Destroying an enemy M-COM (500, Rush)
• Repairing firendly vehicle (10 per 10% repaired)
• Healing teammates with medkit (10 per 20% healed)
• Spotting an enemy and a friendly player kills that enemy (10)
• Headshot kill an enemy (10 bonus)
• Destroying an enemy's explosive (20)

Source: Premium Guide