How to maximize summoner XP gain in League of Legends?

What is the most efficient way to gain experience in LoL?
How is experience gain calculated? I've heard Dominion is better for experience than classic; is that true?

Solution 1:

To maximize XP gain:

• Buy XP boosts. You can stack duration and per win boosts.
• Play PvP instead of AI
• If you insist on AI, play intermediate instead of beginner
• Surrender if you can't win (to maximize games played)
• Invite friends. Referrals give bonus IP, which help you win (and get more exp)

However, I don't recommend trying to level up quickly. IP is much more important for buying Tier 3 runes, and your time is better spent maximizing IP gain.

Exp calculation:

Current (July 2011) formula for XP winning a Normal game at level 15-19 is roughly 3m+25, where m is the number of minutes the game lasts, capped at 198. Intermediate Bot games at level 10-14 use the same formula. At level 15-19, Intermediate Bot games subtract a 25% penalty from that formula, and give XP for only the first 180 minutes a day of play.

Solution 2:

At the very beginning of the game, you are promoted fast. At lvls 19-20-21 you play all day long but it is in vain, but after being 21 lvl, again, your lvl starts to promote rapidly. Also you gain bonus XP per the first win of the day. After a first victory, you had better play dominion but if you want, because dominion might cause some unfairness due to your team's inability to re-group or lasting short time. Nevertheless you should not worry about gaining XP because, in one day, you will be 30LVL and enjoy this game more!

Solution 3:

Dominion isn't the best way to get XP fast. If you win, an average match that lasts less than ten minutes will give you 37 XP, and an average 3v3 match that lasts less than 20 minutes will give you 87 XP.

But the most important factor in leveling fast is playing a lot, and my suggestions is to play what you like the most. That way it doesn't get boring.