In Mass Effect 2 for Xbox 360, there are a couple of ways to get extra levels and experience for your new characters.
Start at Level 5 – Import a level 60 character from the original Mass Effect game
25% Experience Bonus – Start a new game after beating the game at least once
4k Experience Points – Import a level 60 character from the original Mass Effect game
2k Experience Points – Import a level 50 character from the original Mass Effect game