The main goal of Ballistic is to remove blocks before they reach the line at the bottom of the screen. All blocks move down by 1 row after every shot.
The number on each block displays how many times it must be hit by a ball to be removed. To optimize your clear speed, you want to collect as many additional balls as you can; the earlier, the better.
For example, a good start to the game may look like this:
After several good turns, you will gain a decent amount of extra balls for each shot. Make sure that you are removing the maximum number of blocks with every shot.
If you see a tight path to the top of the screen, make sure that you use it! Bounces in a relatively closed area can dramatically reduce and remove blocks, even with relatively few balls:
When there are multiple blocks on the lowest row, the best solution is to shoot at the lowest angle possible. In most cases, 2 wall bounces will be able to clear most of the nearest blocks: