Generally, there's a few easy ones to look out for
Country roads often have semi-circular pull-ins, where there are some trees between the road and the parking place. These make a good place to stop in some cases, but be careful, because you could be mistaken for a 'red light' van. Google red light if you don't know what I mean. I stay in these mostly when my boyfriend is with me.
For this reason, I prefer to stay in small villages in a free parking area, where there are other people around just in case for any reason I start to feel unsafe.
Croatia
15km south of Zadar there is a huge boat Marina with a small beach around the corner and at the end, a private place for 1 camper with a high wall right next to the sea.
To receive my list of great wildcamps around Europe, email me on rachaelpage@me.com with the subject 'Wildcamps in Europe'