When an enemy has locked onto your ship, it’s prime time to deploy your shield. If you have no shield energy left, bank sharply into the nearest corner - this can sometimes shake off the incoming missile.
Some tracks have shortcuts which you should memorise and use to your advantage.
Sometimes it’s a good idea to drop back and allow everyone to overtake you - at least then you have plenty of targets to aim for, and taking down enemies grants a nice points bonus.