There are two rows of red balls. They can easily be dodged. Shoot once each time they come towards you, then another time while underneath. You should make this within 15 to 20 seconds.
There is one giant blue ball waiting at the top. It will bounce between the two platforms. Those platforms can be shot for a power-up. The ball splits into three more forms before disappearing. After the first shot you also get a power-up already, which should help to speed things up.
Start by running to the right. The right row of balls falls strangely to the left side. Once they are on the ground they will do much smaller bounces. You can run underneath them and take at least two shots. But they are also really slow so you can take at least three of them out if you stay on one side. Be careful in the corners, as they tend to take a long time to turn around and you don't want to be stuck with them.
Those clear blocks can be shot for power-ups, but you also get some from the second ball-popping. They tend to be really fast, so try to find a sandclock quickly.