To find miles of sandy beaches head straight to Pescara and drive up or down the coast road from there. In Pescara itself pedestrians are everywhere and progress is slow so, once you've found your beach, you can find a faster route back from a different motorway exit if you want to avoid the crowds. Once the sun has been out for a while the water is warm - even bath-like in the shallows by afternoon on a sunny summer's day.
Montesilvano, slightly north of Pescara, has all beach facilities: umbrellas (usually about 15 euros a day to rent), cafes, bars and restaurants with beach-side showers (buy a token from the bar and remember 'caldo' is hot in Italian, 'freddo' is cold). It's easy as a first space to explore as, if you get there by 10am, you can usually find free parking right opposite the beach. Be careful not to park in scooter or disabled spaces. In Italy in general, a blue line around a space means you have to pay. Disabled spaces are clearly marked and usually have a yellow border. Slightly further north is Pineto, where the beach is bordered by trees giving some very welcome extra shade.
You can also go down the coast to be even more spoilt for choice. By the time you get to Ortona you can find rocky coves.