New Super Mario Bros. Tips

Some tips and Cheats
How to play as Luigi:
When selecting your saved file hold L and R then press A and you will here Luigi Say "Luigi!"

How to get Unlimited Mushroom Houses:
You Must Unlock every level and complete them at least once then all the mushroom houses will remain there and will not disappear when you finish in them
(note: this is an easy way to get as many lives as you want, also you can get unlimited Mega mushrooms and items)

Item Priority:
Items have priority over each other and this is how they go (from littlest priority to biggest)
Blue Shell
Mini Mushroom
Mega Mushroom
(Note: a way of getting alot of points is having a high priority item in your pocket and getting a less priority item)

How to get all 3 stars next to your save file:
There are specific things you have to do to get stars by your save file:

1st Star: Beat the game once

2nd Star: Finish all of the levels once

3rd Star: Unlock all of the Cannons, Pipes and Mushroom Houses, Collect all of the Star coins and spend them all

How to get to world 4 and 7:
You may notice when playing the game you don't go World 1-2-3-4-5-6-7-8, it goes 1-2-3-5-6-8 and you're also wondering how to get to worlds 4 and 7:
World 4: Defeat the World 2 boss as Mini Mario/Luigi
World 7: Defeat the World 5 boss as Mini Mario/Luigi