Keep your distance and follow their car as far as you can do safely. If you lose them, keep track of where you lost them, and the time of day. On your next attempt, you have two options. Option one is sometimes tricky: to start again shortly before the time and place that you first lost them; by watching for their vehicle on the road. Option two is easier, to again follow their vehicle right from the start, and initially stay further away from their car, and then get really close to them, shortly before the place that you lost them before, and then fall back again to avoid suspicion.