There are all sorts of places available, some nice, some convenient. The POI from the Wildcamping website is good, but there are lot of laybys in there and a few places that you look at and think, "really?".
I like forestry car parks and isolated places by the sea. But I've also been found in ferry port car parks and motorway services when needs must
Here's a few pictures of places we've wilded.
FoD. Lots of little car parks about.
Welsh coast.
Irish coast.
Pincnic area in the woods.
Forestry commission car park, Brecon.
We always do a litter pick around the area we're camped in, leaving the place tidier than when we arrived. We also try to make use of local shops (independent ones, not Tesco!)
Hope that inspires!