What's the strategy in agar.io?
One of the first things I realized is that a very small cell can safely hide near the largest cells in the game. Since the larger a cell, the slower its movement, the small cells can use the larger ones to shield them without risk of being devoured. Kind of a host/parasite relationship. Just eat their scraps until you're large enough to go out on your own.
There are many other little nuances you'll pick up on, but I won't spoil it!