Bulgarians are not very adventurous when it comes to dining, and restaurants -- be they upscale, traditional mehanas (taverns), informal diners, or sidewalk cafes -- tend to serve the same menu, with small regional differences, throughout the country. Food varies between good and incredibly delicious; location and price are not good predictors of quality or what arrives on the plate. A much better bet is to look for places that attract what clearly is a local clientele, despite the ubiquitous plastic chairs and/or lack of obvious ambience. In fact, the only bad meal you're likely to come across is in an upscale (and empty) restaurant featuring a fancy fusion menu.
One of the best things about Bulgarian restaurants is that they don't define lunch or dinner time -- most open at around 11am and you can order anything anytime after this. Note that plates are served as they are ready, so don't expect courses to arrive at the same time. Also, if you eat at a mehana, portions are often small; for a full meal, choose a few items. Service is sometimes atrocious, but don't take it personally and make sure you check the bill carefully. A 10% tip is expected, but a service charge is often included. Most places have an English translation of the menu, but descriptions are general, making the choice, given the enormous length of most menus, difficult. If lost, order any of the following stalwarts, featured on every menu across the land: Tarator (cold cucumber and yogurt soup, with chopped garlic, walnuts, and dill); shopska salad (cucumber, tomatoes, spring onion, and red pepper, topped with grated white cheese, not unlike feta in taste, and an olive); kebapche or kufte (respectively, finely spiced barbecued sausage or meatball, often cumin-dominated, and prepared over coals), ordered with "garnish" (potatoes or vegetables, and/or bread -- ask for the bread grilled), or try parlenka, the local pizza, or patatnik, a Rhodopean specialty in which the potatoes are grated and pan-baked with onions, egg, goat's cheese, and herbs); shopski cheese (a creamy cheese, tomato, onion, egg, and mild chili pepper bake); mish mash (a surprisingly delicious egg, cheese, and red-pepper mix); or burek (red peppers or zucchini stuffed with a feta-type cheese, spices, and egg). Other typical items on the menu include kavarma (individual casseroles of meat, at its best melt-in-the-mouth tender, baked with garlic, onion, peppers, and mushrooms in a traditional earthenware pot), sarmi (vine leaves stuffed with rice and tender spicy minced pork and covered in dill-infused strained or thick yogurt), and moussaka (a Greek dish of minced meat with eggplant). Bulgarian breakfast is comprised of banitsa -- a flaky pastry stuffed with salty white cheese -- and espresso or boza, made from fermented millet; the latter is an acquired taste.