If it's in north Wales:
1. Park on a village street, not in some remote layby or rural car park.
2. Park where there are no restrictions, obviously.
3. Park where there is street lighting rather than unlit.
4. Very important: make sure your car is within plain view of occupied properties. Welsh village folk are usually very observant (some call it nosy).
5. At the same time, don't upset the occupants by nicking the space they always use.
6. Crime might not a part of everyday life as it is London (I'm in the slum of Harrow) but nevertheless they still get it, particularly drug-related crime in the big towns along the north coast. Avoid Rhyl in particular, and Wrexham too, while some areas of Caernarfon are a bit dodgy.
The above points probably apply to the rest of Wales too.