Bring a raincoat no matter what time of year. In the summer, there’s no reason not to camp; however, be warned that many campgrounds fill up. Some take reservations and it’s worth making them in the summer.
Get away from your car and into the backcountry. Since Olympic National Park is 95% wilderness, it's hard to really see much of the park without hiking. Furthermore, there’s a law of physics for all national parks (the 2-80 Law) that states if you can hike two miles away from the parking lot, you'll get away from 80% of the people.
Here are some resources to help you plan your visit:
- Here’s the National Park page for day hikes in the park (and their official list [pdf] of day hike trails).
- Here’s the official list of campgrounds in Olympic National Park.
- Here’s the National Park page for general backcountry and wilderness camping. Here's their list of wilderness trails and information on the Wilderness Information Center, which provides the required permits, maps, and bear-proof food canisters.
- Here’s the current conditions on most trails in the Park.
- You can also find some more of my photos from this area on my photoblog.
Have a great trip!