Bulgaria is a modern, peaceful and well-ordered country.
Theft is not as much of a problem as it is in some countries but, obviously, look after your belongings and watch out for pickpockets in busy markets and on crowded buses. Prime targets for thieves are parked cars, especially those with foreign licence plates and/or rental-agency stickers. Never leave things inside the car; always lock everything in the boot, or take it with you.
Bulgarian drivers can be extremely reckless at times, and pedestrians should be very careful when crossing roads, especially in Sofia. Cars regularly park on pavements, blocking them for pedestrians. Inevitably, footpaths in towns throughout Bulgaria are often crumbling and under sporadic repair.
Bulgaria has harsh drug laws. The country is a common route for drugs (and arms) smuggled across the Black Sea from Russia and Armenia, and from Turkey, so always treat the transport, trade and use of drugs with a great deal of caution.
Bulgaria is a major producer of tobacco, and smoking seems to be the national pastime. Cafes, bars and restaurants are often poorly ventilated, but this is less of a problem in summer when most patrons sit outside.
Construction work along the Black Sea shows no sign of slowing down, and many places currently resemble vast, dusty building sites. It's not easy to know when current work will be finished and where new projects are about to begin, but by law, construction should not be taking place during the peak tourist seasons. For now, if you want to avoid the mess completely, you'll need to scout around for somewhere more to your liking; there are still quiet nooks to be found.