Keep the green rectangle inside the screen. Orange obstacles are obstructing you: avoid them. Grab the blue powerups: they'll allow you for example to become invisible. When your teleportation meter is completely filled (=white), you can use teleportation. When you activate the speed mode, you'll earn even more points. This is also the case when you move in a straight line or backward or when you stay close to the left or right borders of the screen.
Use the mouse to move the green rectangle. Hold the spacebar to activate the 'speed mode': you'll earn even more points.