A fair bit of info already out there if you invest a few moments searching around for it. Several threads over the past few years located here on Spey Pages. Quick and dirty:
1. Have realistic expectations...for someone not familiar with these rivers or winter steelheading, simply hooking one winter steelhead on a swung fly during the week could be considered a good trip.
2. Weather...your trip could easily be a write off so be prepared for that.
3. Settle into one spot/river/stretch, find good water, and learn how to fish it. You WILL be distracted and tempted to chase reports or new scenery, but it will most likely not increase your odds of catching fish.
4. Be prepared to deal with crowds.
5. If you are a novice rower and plan on floating you'd be well advised to avoid the Sol Duc and Calawah without "seasoned" guidance.
6. If you've never fished the Olympic Peninsula, only have a week, and are truly interested in catching a steelhead on the swing, you'd be well advised to seek the skills of a respected guide out there.