Asides from doing the obvious (listed these at the end later) this page gives the best tips for increasing agario performance and making it run faster. As the majority of people use Windows this guide also shares some brief tips on how to make that run faster.
How To Reduce Lag in Agario
1.) Use Chrome Experimental Features
First up, enter in the following address to your web browser, which should then take you to an experimental features page where you can make some important changes to make agar faster.
Use ctrl-f to find, now you can make the following changes to this page:
EXPERIMENTAL CANVAS: Enable
ENABLE GPU RASTERIZATION: Force-enabled
NUMBER OF RASTER THREADS: 4