Recently I have been playing this game quite a lot, and while I have never managed to get a high score, I stil think I have some valuble tips to share with you
At the start of the game, when the Donofruits are moving quite slow, try and collect letters of all the same colour. This gives you a 40 second rather than a 20 second bonus. Don't bother later in the game, just be glad for any extra time!
The more you play, the more likely you are to see the higher rank Donofruits. Fish gives you 100 points and rainbow gives you 50. Gold and Silver seem to change.
If you collect more than one donofruit on the same jump, their points go up, so time your jumps well.
Always place the Hasee on the end of the platform, he can move in mid-air to collect more fruits