Everyone says "Protect your front wheel", but what they don't tell you is that by the time stuff gets near your front wheel, it's often too late to do anything about it.
You have to look 3 or 4 places ahead of you - even farther ahead - and watch the general movement. Constantly. The flow should be FOWARD. When people start to move from side to side or when speeds change abruptly (usually slowing), that's when crashes happen. Otherwise, try to RELAX and just go with the flow. Understand that when something happens on the far right side of the pack, it will affect the far left very quickly.
Since this is your first pack start, you may get "shot out the back" in the first mile or so because you're not comfortable with the proximity of others. But if you're able to hang with them, always watch the speed of the leaders and get ready to pass the slower riders in front of you without hesitation. Don't be afraid to tell slower riders to "stick" or hold their line while you pass them.
Do not thumb your nose at them as you pass. That's frowned upon.