When less-than-fresh batteries are used, power drawn for the wheel motors can cause the servo motor to droop. While this may make for cute-looking behavior as though it's shaking its head when reversing away from things or changing direction, it's not ideal and means there are voltage drops as the motors pull lots of current. This is especially noticeable if you have used alkaline batteries, that are not able to deliver as much current as LiPo batteries can.
A capacitor is a component used to store power, almost like a battery. Using a large capacitor between a ground pin and voltage pin on the servo motor pins can prevent this voltage drop. I recommend a minimum for 470 uF, if not bigger, using an electrolytic capacitor.
The pattern is to use a jumper wire from the servo V-pin to the breadboard. At the breadboard, wire this into an empty column...
