Majora's Mask tips and tricks

Lots of rupees

Here is how you can get a lot of money :-)

50 rupees: Win the game at the Treasure Chest Shop in the eastern district
50 rupees: In a chest on top of the clock tower
60 rupees: On the 2nd day at night, at the South Clock Town Laundry Pool, pick up the three red rupees at the bottom of the water. OR: As Zora Link, use your fins to catch them through the grid
100 rupees: With the Bunny Hood, in the eastern district, climb on the roofs from the northeast corner and jump up to the chest (south on the map - get a new one after each Song of Time)
100 rupees: On the 1st day at 2pm, wear the Goron Mask, talk to Anju at the inn and tell her you have a booking (don't talk to her before!) to get the Room Key. Go to the 2nd floor, open the 2nd door (called the "Knife Chamber") and open the chest
100 rupees: On the 3rd day, go to the Stock Pot Inn from 6pm. Nobody's there and Anju's room (1st one on the 2nd floor) is unlocked. Inside is a chest with 100 rupees
100 rupees: With a bomb, take the passage leading to the Astral Observatory. Go left as soon as you can, swim past the Skulltula, go left and blow up the wall (you can come back after each Song of Time)
200 rupees: At the Curiosity Shop in West Clock Town, sell some Gold Dust won at the Goron Racetrack, a Big Poe's soul or Chateau Romani (in a bottle) to the man at the counter, who offers you a huge rupee!

50 rupees: In the north, get rid of the big Dodongo (you can do it several times!)
2x 50 rupees: At the same place, drop through the hole located next to a rock (not far from the small Dodongo), which lets you pick up two 50 rupees thanks to two more Dodongos (where the Piece of Heart is - thank you Max335
50 rupees: When you got the Light Arrows, go to the south or east part of the field at night. Fire arrows at the blue skulls and pick up a purple rupee for each of these enemies!
50 rupees: The above tip also works with many other enemies
N64: 100 rupees: Once you have won the Piece of Heart with the Gossip Stones, if you do this quest again, you will get a silver rupee. You probably need to be in another 3 day cycle.
200 rupees: In the south, shoot arrows (a good ten or so) at the thief bird
Greg's tip: Wear the Stone Mask so it doesn't see you and aim at it easily!

N64: 100 rupees: After getting the Piece of Heart from the man at the Tourist Office (picture of the Deku king), pay him another visit after taking a picture of Tingle and show it to him. Hw will say that Tingle is his son, will be sorry for the inconvience caused, and will give you a silver rupee.

90 rupees: Break all the pots with your fins in one shot. Stand right opposite the pots and a little at a distance - but still in the light blue zone on the map.
Tip: Play when you have no rupee, this way you cannot lose anything ;-)

100 rupees: In the northeast part, throw your Hookshot at the pillars, cross the bridge, open the door and open the chest

Many: In the Ikana Castle, you get 15 or 20 rupees for each defeated enemy - thank you to 0N1L1NK - (and ReDeads stay still with the Gibdo Mask or Garo's Mask)
4x 100 rupees: In Ikana Canyon, if you got the Light Arrows and at least 16 Heart Container, swim towards west from the broken bridge, cross the waterfall and enter the Secret Shrine. Shoot a light arrow at the sun above the door then speak with the mysterious man. Defeat each enemy in the four rooms (from left to right: three Lizalfos, a Wizzrobe, Wart and a Garo Master) to get four silver rupees!

100 rupees: Near the Stone Tower Owl Statue, turn the temple upside down, go left where rocks are falling, then plant a Magic Bean and climb on it to find a silver rupee (as well as a fairy, magic jars, bombs and bombchs)