The best advice for Trader Joe's? Take your time! This store is such a cool spot and I'm always finding a neat new ingredient or pre-packaged foods/snack that are the unique focal point to a tailgate or house party.
I typically don't like to spend too much time down the frozen aisles, but there is some quality stuff here. Stuffed mushrooms, gourmet mini pizzas, even the spinach artichoke dip is good enough that I bet you most wouldn't question if it was homemade or not. The dairy section has a HUGE selection of unique offerings as well, it's the only grocery store I know of that has Crème fraîche all day everyday! It's a great store to find some inspiration for your next culinary endeavour!
Be sure to check out the back corner for samples, you'll find them cooking up something everyday, including recipes and everything you'll need to make it right there. The bread up front is top-notch, Tuscan Pane is great for pressed paninis. The wine section is full of value as well!
Bring your friends, bring your empty shopping bags, and bring a curious mind. Trader Joe's is such a refreshing experience to grocery shopping.