Subotica reached its golden period during the beginning of the XX century, when the majority of its monumental buildings were built. It was a very important center of wealth, influence and culture. It was the third largest city in the Kingdom of Hungary and subsequently the third largest city in the newly formed Kingdom of Yugoslavia (after Belgrade and Zagreb). As chance would have, having become a border-city its population growth stopped and stagnated at the same number ever since, and now it's only the second largest city in Vojvodina (after Novi Sad) and fifth in Serbia. Because of this, today, Subotica is not a huge city population-wise, and is free of the typical congestion and concrete-jungle feel of bigger cities, but it still nonetheless has a disproportionate amount of beauty to offer and a relaxed pleasant atmosphere. One of the things that hasn't changed over the decades though is its multicultural nature (1/3 Hungarian,Serbian,Croatian), with all the benefits that come with it, among them a unique and vibrant culture.
There are two languages in everyday use in Subotica: Serbo-Croatian(Serbian/Croatian) and Hungarian. The former is spoken by nearly everyone, while the latter is spoken natively by ethnic Hungarians who make up around 35% of the city's population and is also understood/spoken by many others to varying degrees. When it comes to global languages most younger people speak at least some English (many are fluent), but when it comes to older generations (60+) German is more useful. Your best bet with middle-aged people is also English (don't expect fluency).
Subotica is accessible from both Belgrade and Budapest by the fast international train (Subotica is located on its route), that starts its journey from Prague and travels to Belgrade (and vice versa). Via these cities Subotica is connected to most European capitals by train.
There are also 2 daily direct trains from Szeged just across the Hungarian border. This train takes 2 hours, but only goes 45km, and costs under 200 Dinar (~2€). It is a single carriage local train and quite an experience.
A1 motorway (E75), Serbia's longest and most important road, passes through the city, if you prefer travel by car.
Buses are also an option (for example direct ones from Novi Sad, Belgrade, Budapest, Zagreb, Szeged, Sombor etc). They are usually more expensive but are also, more often than not, faster, cleaner and more comfortable than most local trains, and thus definitely recommended unless you want to experience the more unique domestic experience. Timetable.
A detailed map of Subotica can be downloaded from here.
Most of the city's important sights are more or less within walking distance of each other (which is also the best mode of travel through the city for appreciating the architecture and atmosphere). Lake town Palić is accessible by public transport (bus; number 6, stops near Hotel Patria, near the city center). The city bus timetables are available here. A single ticket costs 60 dinars. In case you decide you need a cab (to see some stuff on the other site of town for example, or for whatever reason) there are taxi stations on many locations but the easiest to find are probably the one next to the Town Hall and the one next to the train station.
Subotica's beautiful town hall is surrounded with a number of pedestrian-only streets where people gather and meet, especially in the evening, giving the town a Mediterranean feel. The water-fountains and cafes in the center of the town are a great spot for people watching. The townhouse itself is lit up at night with spotlights that highlight the beauty of the building. It's also surrounded by a small park (the city center is generally rich with vegetation and trees) in which one of the two big fountains is located. There are several galleries. A tour through the Town Hall is also worth doing. There are also many beautiful religious buildings worth seeing.
The town comes alive at night. The street Matija Korvina (off the main pedestrian street "Korzo") seems like the most happening, with a number of popular bars and restaurants (Boss, Stara, Beer&Co). In the summer there are many festivals of music, film, food, and any other excuse creative people can find. There is a large market about 2km west of the center called "Buvljak" or "Ocskapiac" (meaning flea market), where a morning can be gone in a flash. 8km to the east is Palić, an idyllic lakeside town of 6,000 people (take bus no. 6 to get there). The parks surrounding the lake are popular with tourists from the region. There's also a very green and well kept Zoo located in the parks (by all accounts the best in Serbia). There's also a big traditional horse farm/stables/range near Kelebija (a couple of kilometers from Subotica) for those interested in experiencing and ridding in traditional horse carriages.
There are many large supermarkets scattered around the city. There's also a large mall located in a street off the main square. For a more unique experience visit the city's main large market about 2km west of the center called "Buvljak" or "Ocskapiac" (meaning flea market), where a morning can be gone in a flash.
The local dishes are definitely worth seeking out, as they are done really well and are quite cheap as well.
The region's famous fast-food is Burek. It is a pastry with various fillings like cheese, mince, mushroom, etc. It costs about 100 dinars (1 euro), a bit more with "(tekući) jogurt" (a liquid form of savoury yoghurt). Most bakeries will have it, as well as specialized shops where it is made in front of you. An experience not to be missed!
Some other domestic fast-foods are pljeskavica (roughly pronounced as plyeskaveetsa; basically a kind of Serbian hamburger) and palačinke (palachinkeh; European pancakes/crêpes filled with either savory or sweet stuffing, folded in fat/wide rectangles).
Also worth seeking out is "ćevapi" (chevapi), small skinless sausages served in a flat bread called "lepinja".
Grilled or barbecued meats are also a tradition, so they are done masterfully. Look for places displaying the sign "Roštilj".
Also don't leave the city without trying gulaš and paprikaš (traditionally Hungarian, and just generally local, types of meat stews) popular among the locals.
If looking for full service, an upmarket ambiance and international menu, check out Boss Cafe in the center of town; is a really nice place to spend time and the pizza is excellent. (http://www.bosscaffe.com/)
Since the region grows a lot of fruit, a lot of households make snaps ("Rakija") from the various stone fruit, apples, pears, grapes, etc. grown locally. Try to find some that was made for own consumption (and not for sale) for the best quality! Another local specialty is a bitter herbal liqueur called "Gorki List" (various knock-offs are called Pelinkovac, as they are all made from the herb called Pelin, but this is the real deal). It aids digestion, so drink it some time before the meal. There are also traditional wineries near the city if you prefer wine.
Hotel Best Western - Gloria****
Hotel Vila Majur****
Vila Royal Crown****
There is a hostel with clean modern private rooms for 900 Dinar per night. It is behind the station, Segedenski, behind the Economics Faculty at number 14. The tourist information can supply maps and directions too.
If you haven't already included it in your Subotica visit, go check out the nearby lake and lake-town Palić (bus n.6). Otherwise you can take Bus No.1 (in front of the train station) to Kelebija granica (the Hungarian border). From the border you can walk to Tompa Bus station and take busses from there to Szeged, Pécs (via Baja) and Kiskunhalas. Due south is Novi Sad and southwest is Sombor.