If it is your first time, I suggest the following:
Apps:
Lettuce Wraps (no brainer)

Entrees - Chang's should always be enjoyed family style.

Most popular items are the Mongolian Beef, Chang's Spicy Chicken, and Philip's Lemon Chicken.

Less popular, but fantastic: Shrimp with Lobster sauce, Black Bean Chicken. The black bean chicken might be my favorite thing on the menu and it brings a salty blend to otherwise sweet and/or spicy dishes. Also, their orange peel dishes are excellent.

Best noodle item is the Dan Dan Noodles (but they are a bit spicy). Lo Mein is also very good.

Best "off menu" item? Firecracker Shrimp

their fish dishes vary depending on availability, but they are very good at cooking their fish, so you can't really go wrong there.

Items to avoid: Sweet and Sour Chicken, and any curry dishes.

For desert, I personally like the banana spring rolls, but the great wall of chocolate is amazing as well.