How to get 3 stars????

I have played many time-management games and ALWAYS manage to eventually get 3 stars on all levels.
But with the Incredible Dracula series, I struggle to get 2 stars on most of the levels.
I got 3 stars on all of the earliest ones, but after 11 I have only been able to get 2 stars.
I have the Collectors Edition of these games, and I've tried following the guide precisely as they suggest, but I've played some levels over and over and over, and I feel lucky to barely squeak out 2 stars.
Does anyone have any suggestions about what I'm doing wrong?
I DO use all of the bonuses & boosts as soon as they become available. It just never seems to be enough.
Thanks for any tips you can give!