General rules: You may not fly over people, not over crowds, not over private properties, not over cities, not over nature reserve and national parks, schools, hospitals, jail, industrial and military settings and any “sensitive infrastructure”, medical or police operations, accidents etc.
You need to have a special insurance for your drone that covers damages caused by the drone up to at least 3 million euro. (depends on the country though)
Special rules for the countries:
First of all, I haven't found anyone who could tell me if it's allowed to fly a drone in Italy. In the flight regularity of the ENAC are contradictory statements. Combined with my crappy Italian... I couldn't figure it out. Also some Italian friends couldn't. But some Italian ex-member (Who could that be?) Told me to just go ahead.
So, as I understood it, you can fly up to 70 meters in height and 200 meters in distance. (Without having a license)
The rules have changes in the past few month a lot. So at the moment, you are allowed to fly via live view on your controller. (Before 2 month this was forbidden, only sight-fly was allowed). In Germany, you can fly 100m high and as far away as you want. But after October you have to label your drone with a 'heat and fire resistant' plate with your name and address on it.
Switzerland: Here you are allowed to fly up to 150meters but your drone has to remain in your field of view.
^ These are only the rules for drones weighing less than 2kg and more than 500gramms.
I used the Phantom4 from DJI. Pretty awesome drone. I can only recommend that thing. In some shots, it was quite stormy (wind up to 30 mph) but as you can see, the drone didn't have any problems.