In SM64, in Snowman's Land, I always thought you could only get to the shell by spinning off of a head hunter's head, but you can shoot to it with the cannon, with a little aiming.
You can also shoot to the caged island in Whomp's Fortress, or else use the owl in the tree a little to the left of where you start in that area.
Also in that level, at the bottom of the tower, I'm not sure which side it is(possibly the side in the shadow of the tower), you can punch the wall and there is a 1-up in a little alcove.
In Lethal Lava Land, if you turn around directly at the start of the level, you can long jump to the island with a flying cap, so you can get around the level more easliy.
In Tall Tall Mountain if you turn the other way at the very beginning of the level and long jump from the edge of the ledge with the 1-up, you can catch the wind and skip going around most of the mountain.
It IS possible to get all the stars in Tick Tock Clock with time frozen.
In Rainbow Ride, for the star "Tricky Triangles", instead of stepping on every pyramid thing, you can just go to like the third one and backflip up to a higher one, giving you a few more nanoseconds to avoid running out of time.
When you play the strange level/area thing where you have to get the red coins on all the clouds, grab a new flying cap every chance you get; you wouldn't want to lose the flying power in mid-flight and fall from the sky to the outside of the castle and go all the way back up to the third floor to try again.