Hengistbury Head, or Chesil Beach are probably the best bets. We prefer the Portland end of Chesil, although many prefer the Abbotsbury end, both have large (pay) car parks.
Best times to go evening/night. During the day things tend to be quite quiet unless the mackerel are running along Chesil. Use feathers, cast as far as you can and jag the feathers in.
Best baits, live peeler crab, live sand eel, lugworm, ragworm, mackerel.
if your after some good local advice try sea-fishing.org theres plenty of helpful people on there they may even meet up with you and show you good spots
Cheers Dave