Your aim is all about your connection.
If your barely lagging, then aim just a very small amount infront of the enemy
EX: If they're running towards your left, shoot to the left and aim a little more to the left then where the person is
Also if the enemy is too hard to shoot, then aim for where you think he's heading
If you guess right, then most likely you'll hit him once or twice
This trick applies with nades to and actually works even better
Aim in the direction the person is running and throw the nade a little bit further in that direction than the guy running. With the nade you can throw it even further ahead and it will still hit because the explosion is so big
Try it out guys, let me know how it works for you
