For spring break in the Olympics, you have two options: (1) one of the long, low elevation river valleys, like the Hoh or Enchanted Valley and (2) the wilderness coast. The latter is awesome but also extremely rugged and requires paying extremely close attention to tide tables. Many of the headlands have to be rounded at low tide. Be aware that with minus tides (lower than average low tides), the corresponding high tide will flood the entire beach. Wherever you go, it will be wet, so take good rain gear!
Note that bear canisters are required for food storage on the coast (more for aggressive raccoons than bears) and any place inland that doesn't have bear wires. You can rent them from the Park for a nominal fee.
Read through the excellent trail descriptions on the ONP website (nps.gov) and contact the Wilderness Information Center in Port Angeles for more info. You'll need to get backcountry camping permits.
You might also want to check trip reports on
www.nwhikers.netI read on nwhikers.net, but can't find the info now, that access to the Elwha Dam is closed while they're working on removing the dam. You might want to check when you talk to the Park Service.