On the spot
Stop, secure the scene and put on your high-visibility vest before you step out. Warning triangle behind the car. If anyone is hurt, give first aid according to your ability and call the emergency medical service.
Then exchange details with the other driver: identity, and the details of the vehicles involved.
Police, or a joint record
Czech law requires you to call the police when there is injury or death, when the damage clearly exceeds CZK 200,000 on any one of the vehicles including the things being carried in it, when somebody else's property was damaged, when a part of the road or its equipment was damaged, or when the participants cannot get traffic moving again without disproportionate effort.
If none of that applies, the participants write and sign a joint accident record instead. It has to state where, when, why and how the accident happened, what the consequences were, who the participants and vehicles are, and include a sketch or photographs.
Photographs are worth more than memory
Before anything moves, photograph the positions of the vehicles, the damage on both, the road, the signs and any traces. Claims are frequently decided on exactly what these show - and nobody remembers the details three weeks later.
Afterwards
Report the accident to the insurer without delay. If you caused it, the claim is settled from your compulsory liability policy; if the other driver did, you claim against theirs. Damage to your own car when the fault is yours is only covered if you have comprehensive insurance.