Playa San Juan sits on the TF-47 coastal road on the southwest side of Tenerife. From Tenerife South (TFS) airport it is a 40-minute drive: take the TF-1 motorway south then west, exit at Adeje, then follow the coast road north. Taxis from the airport run around 50 to 60 euros.
By bus, TITSA line 473 runs along the coast between Los Cristianos and Playa de las Américas and continues to San Juan; line 473 also continues north to Los Gigantes. Service is roughly hourly. A hire car is the easiest option if you plan to explore the south or visit Teide National Park inland.