Here are some tips that get 3 stars.

To get three stars for each level, you should try to pop the bubbles as much as you can without any disruption in between. In other words, the more consecutive poppings you make, the higher score you will get. Dropping a lot of bubbles while keeping combos uninterrupted is another way to score higher origins.

In summary, the more combos you can accumulate or drop a lot of bubbles, the higher your score will be.