Cable management on your Prusa i3 kit, or any 3D printer kit, is very important in order to prevent failed prints and other cable related issues. The following guide is intended to assist with cable management on your printer.
On the extruder, gather all cables together just above the X-carriage. Small cable-ties are useful here. 
Bring the cables through the frame and down towards the RAMPS board top left corner. 
Secure the extruder wiring to the top left RAMPS mounting screw with a small cable-tie.
Bring the extruder wiring bundle down to the lower left RAMPS mount and secure. Trim the red hot-end heater cable to length and insert into heater screw terminals. Bunch excess thermistor and stepper motor cable under the Arduino board. Connect Thermistor, Extruder Stepper, Hot-End Fan and (optional) Auto-Level Sensor Cables to the RAMPS board and reinstall the RAMPS fan.
