Do not reverse from a side road into a main road. When using a driveway, reverse in and drive out if you can.
If a vehicle ahead swings out to the left or the right particularly at the entrance of a side road or a mini-roundabout they may well be attempting this manoeuvre and represent a developing hazard.
As the vehicle ahead starts to take an unexpected path or position click as it may well be trying a U-turn or another manoeuvre.