Tips & Tricks #1 on Agar.io
#1 Use the boundary to your advantage!
Hugging the boundary is important for when you want to escape from a predator cell - particularly when there are solid virus cells that you know can protect you. At least 1/3 of your cell can overflow outside of boundary lines, which leads to an easy escape otherwise seemingly impossible. You cell does not burst, or pop when you hug the borderline, and hence becomes a crucial strategy to know to survive. On the other hand, the Agar.io game space does have its limits, and if you know where those are, you can use them to trap or corner your opponent. If you corner a smaller blob into the edge of the game, you'll be able to absorb him easily because he'll have nowhere to run. Learn to use it to your advantage
#2 Time your splitting carefully!
I know it's tempting to split your single cell into two to go after smaller prey, but it's not always worth it. And you need to be able to gauge the size difference between yourself and whatever you're thinking about eating because you go down to half your size when you split. Only split when you can guarantee that you'll not only be able to hit your target but that you won't be too small to eat them once you do. It's also almost always best to split when you can eat more than one target, making your splitting extra worth it. After you split kill and are in a corner, try to focus all your mass in one cell by pressing W. That way, if someone kills the small cell, the loss is not so great, and if they are small enough, you can eat them.
#3 Be extra careful when more than two cells!
You almost never want to split up too many times at once, unless you're trying to get away from bigger cells or it is guaranteed that you'll get much larger. This is particularly the case once you've gotten enormous. Each time you split, your cells are halved in size and doubled in amount. This means you're less capable of hunting down smaller cells, and you're very vulnerable until your cells join back together. Splitting too many times is one of the biggest causes of falling off the leaderboard, second only to getting cornered and trying to juke through virus cells or having someone spawn a new one on you. Only split when last resort, to save your life. By doing that, all your cells will be very small, and you'll have a hard time controlling them, giving your enemies an opportunity to finish you. Other than that, the more cells you split into, the more hostile cells will be able to consume you.
#4 Hide behind viruses!
So, while you're small, you'll often see the aggressive larger blobs coming after you to eat you up. If one is in hot pursuit and you think you can't get away, but a virus is nearby, that may be your best hope of survival. Big blobs don't like viruses because once a blob is larger than the virus the virus can split it into pieces if they collide. By hiding your blob behind the virus, you'll keep the larger aggressive blobs away from you.
#5 Virus cells as a weapon!
Those spiked virus cells aren't just there to make life difficult when you get big, you know. They can also be used as hiding spots when you're smaller than they are, and they can be used as weapons against larger cells. When you're larger than an obstacle cell, and you collide with it, you split into several smaller cells which are what makes them the number one size-ruiner; but you can use them to your advantage by shooting mass towards them. The 'W' key expels mass in the direction you're pointing the mouse, meaning you can aim mass toward an obstacle cell. And what happens when you shoot a bunch of mass into one? It spawns a brand new virus cell in the direction you were aiming. This is something you need to take advantage of when there are several large cells on the map, or when you are large and are trying to defend yourself from an even greater cell.