If you intend to survive in the mania of the cell stage, then you need to be quick on your feet. Be ready to duck and weave between other organisms. If you are being chased by a bigger carnivore, then give them a herbivore to attack instead. You could also drag them into the attack range of any of the even bigger creatures around.
As soon as you can, put a spike on your backside. This makes it impossible for carnivores to attack you from behind. They'll just ram into your spike and hurt themselves. Electricity also works well for this purpose.
If you are a carnivore, you should also remember to put spikes by your mouth. This will drastically improve your attacking power.
If you are having trouble getting enough food, then you might want to put mouths on your sides. This will let you snatch food while you are moving through the level. This should really speed up your growth.
This goes without saying, but keep an eye out for any big explosions. This usually signifies a bit of meteorite being broken up. Swing over to the glowing spot to see if there's collectible DNA.