Pike Place offers some of the best food and ingredients in all of Seattle. It's a great place to go for lunch or to pick up every ingredient you would need for a great dinner. The market is also full of some amazing art and fun nik-nacks.
The market is a bustling place full of tourists and locals alike. To have the best experience remember your manners, don't stand in the middle of the walkway, and don't walk with multiple people abreast. Be sure to check out the shops downstairs. My personal favorite is Golden Age Collectibles. Be sure to bring cash to the market.
If you don't want to seem like a tourist, DO NOT TAKE PICTURES OF THE FISH THROWERS. You're just annoying everyone. Don't do it.