Its quite a trip out there but so very worth it if you wanna have the very special beach-experience! You can go there by car and then take the ferry either to Pines or Cherry Grove (I would prefer Pines!) or you do all by public transportation - there a "getaway tickes" for 36Dollars and the transfer works really smooth - may even be faster than by car!
I often run to this place and I love this perspective on glittering Manhattan and the feeling of coolness in the air from being so close to the water. To sweat and breathe and see this view of New York gives me a sense of being in this great City.