Hint :
Never Lose Kudos:
When you about to lose in a race, press A, B, X, Y, and Start at the same time so that you will go to the title screen. Go back to your last save and you will have the same kudos as before. Don't try this during the second stage in a championship race.

Earn 1000+ kudos:
In every chapter, you will be given 2 hotlap races. They are the easiest ones and they dont have time limitation. You will be required to beat a lap time in one of those 5 laps per race. First you set the lap time required to max (it is default) then in the first or second lap you have to beat the time (its so easy). Now you have 4 more laps. Now you can do as much tricks as you want, no time limitation. You can spend 5 or six minutes per lap executing tricks, I mean powerslides. Just speed up and turn left or right with the handbraking a "k" will appear on the screeen. (That means that you have made a trick). You can go backwards to have more place to do tricks. Execute the trick as much as you want and when you finish the race you wont believe the kudos you have earned. I achived the required time in the 1st lap then then tricked for about 8 minutes and I earned 3000 kudos plus a joker. By using the joker again (joker doubles the kudos) made 6000.