I'm a first-time mom and we just went on vacation with my 3 month old and got back yesterday...here's my advice...
Bring enough formula for a day on the plane...a friend of ours was on a flight that was delayed for 4 hours and she almost ran out of formula (her flight was only supposed to be an hour). Although our flight was not delayed my daughter wanted to eat more than usual (needed hydration maybe?) on the flight so I'm glad I had the extra formula in her bottle. I fed her as the plane took off and landed she did not fuss at all about the cabin pressure.
Get the ready to use formula too -- a lot easier on a trip
If you are still using a carrier/car seat and the baby is not ready for an umbrella stroller --- get the stroller frame. Ours was the graco one and about $50 but worth every penny. I was able to keep her in her car seat (which you do NOT want to check with your baggage!!! If that gets lost you are stuck at the next airport unless whoever picks you up has one) and wheel her right up to the gate. Left the seat and stroller frame at the door of the plane. The frame weighs about 12 pounds and much easier to carry than the standard stroller.
I had a plastic bag in my carry-on diper bag ready to take out immediately -- it contained a bottle, pacifer w/leash to attach to her shirt, 2 diapers, trave-size wipes. sleeper and onesie, toy, small blanket, baggie for stinky mess, and a magazine (for me). that way I wasn't searching for anything and could sit right down.
Stay as calm as you can...Our flights were on a 50 seater plane my daughter seemed to get upset and fussy when we walked down the aisle (we had seats in the last row of the plane both times) but once we settled into our seats she was fine...looking back now I think she was feeding off of my anxiety of flying and it was higher than it normally is b/c now I have her. I also think she felt my nervousness -- people gasped and made comments when they saw an infant entering the plane and again, I know she felt my stress.
We had a lot of turbulance on one flight I just smiled and made funny faces at her the whole time and she didn't seem to notice the plane shaking since she was focused on my face.
In general, just roll with whatever happens, stay as calm as you can and be prepared for any situation. Best wishes and enjoy your trip!