Easy Staff Ghosts!

First of all you need to race on a motor, a fast one. Because you can't make any mistakes here, so you don't need the acceleration. Motors just race better, you can make way better angles going through a corner. What I found to be the easiest tracks:

Easy Ones

• Luigi Circuit (time around 1:26 unlock its)
  
• Moo Moo Meadows (time around 1:32 unlocks it)
  
• Toad's Factory (time around 2:12 unlocks it)
• Mario Circuit (time around 1:39 unlocks it)
• GCN Peach Beach (time around 1:30 unlocks it)
• DS Yoshi Falls (time around 1:22 unlocks it)
• N64 Mario Raceway (time around 2:07 unlocks it)
• GCN Donkey Kong Mountain, this must be the easiest of them all, I beat the expert ghost by 5 seconds on this one, after some practice ofcourse!
• SNES Mario Circuit 3 (time around 1:33 unlocks it, if you're good at drifting this is no problem at all)
• GBA Bowser Castle 3 (time around 2:47 unlocks it)

A couple tricks that will help you on the way.

1. Don't have a quick start? Restart!
2. Made a mistake? Restart!
   
3. Perform a weelie on long straight ends for extra speed, it helps.
4. If your own ghost is faster than the default computer ghost, race against your own ghost.
5. Use your speed ups at the right places!
6. If you really can't make it and get ass kicked by the default ghost or you just barely beat him/her, then you can watch the default ghost replay. See where he uses his speed ups, where he cuts off, where he starts drifting, etc.

Hope that helped!