Firstly all wires should be as short as possible without being under tension. The reason for this is that the shorter the wires are, the less resistance there is from one end to the other. RESISTANCE= POWER LOSS.
Wherever possible, allways do away with connectors to the motor, and solder the wires on. (hardwireing)
The other thing that nearly allways causes trouble for people starting out is having power leads near the reciever wire.
The power leads generate electro-magnetic interference, and if the reciever wire or reciever itself is next to them you will be sure to have your car behave very strangely! If you get interference ALLWAYS stop, and check your car over. If you dont, you could either hurt someone, or destroy you car!