The important thing is to try and keep one of the meteors in the air for as long as possible. Avoid the extra turret power-ups, keep shields going, and be patient.
A bit of a walkthrough:
1: Just find one of the larger eggs and fertilize it.
2: Combine all of the same colored cells and push the combined mass upwards a bit.
3: Move the embryo towards the bottom of the screen. Hug the sides to avoid the tailed organisms.
4: Wrap the tentacle around a bit of food and pull it into your "mouth."
5: Click the "intestine" to make the embryo move up. Clicking the left kidney turns the embryo left, and clicking the right kidney makes it turn left. The tentacles will pull the little organisms into your "mouth." Repeat.
6: Shoot the little "arrows" at the other embryo. Your mass will increase, but this is okay.
7: Drop eggs into water, fly about.