Since a silver star allows you to rotate it and the six surrounding pieces as one unit, it is much easier to make your second and all following flowers around a starflower. Not only is it easier to make flowers around a silver star, but you get more points for this than for making a flower around a normal piece.
When making flowers, try to make as few combos as possible. As you make more and more stars, be extra careful when moving pieces not to make combos from your silver stars.
Note: There are two types of black pearls. One moves other pieces like a Y and the other like an upside down Y. The latter is the more useful of the two, and having one of these pearls to use inside the grid is very helpful for rebuilding the grid.
Below is a table showing the score for different types of combos. Each score in the list is for each level beginning with level 1. Click on the title of the combo to see what it looks like.