You start out as a small fly, and as you eat more food, your level goes up. As you level up, you start to eat other people as well. At each level, you get a new special skill and more food. The answer is easy: you can either fly or die.
Eat things and animals with a green border. Animals with red lines around them will eat you. You and hundreds of other players will be fighting to stay alive, so make sure you keep moving and keep eating. Watch the water level as well, because you'll need a lot of water to stay alive.
As you play the game, each animal will have a special skill that is unique to it. You can move through the game faster if you use that special skill. You'll have "beginner's luck" when you're a fly. This gives you a 50% chance of not getting attacked by an animal. Make the most of the special powers.
Have fun and good luck!