A good way to get your bearings on your first day in the city is to take the city tour bus. The buses run every 20-30 minutes between 9.00am and 5.00pm, and with a 24-hour or 48-hour ticket, you can hop on and off as many times as you wish. Taking the sightseeing bus will give you a general overview of the city and make it easier to decide where you'd like to spend more time during the rest of your stay.
Hop off the bus wherever you fancy, and explore the area, then take the next bus.
Now you've worked up an appetite, dinner at a traditional parrilla (barbecue grill) provides a fitting welcome to the city. Barbecued beef is one of the most popular dishes in Buenos Aires. Start with a grilled provoleta cheese, then move on to a steak like asado de tira or bife de chorizo, accompanied with fries. In the Palermo neighbourhood, you can choose between La Cabrera (Cabrera 5127), El 22 (Carranza 1950), Río Alba (Cervino 4499), and Don Julio (Guatemala 4691).
After dinner, head to a neighbourhood milonga (social dance event) to see locals dancing tango. La Viruta (Armenia 1366), is a popular option. Others nearby include Villa Malcom (Av. Córdoba 5064) and Oliverio Girondo (Vera 574).