Check the airline / BAA website for the latest on stupid hand baggage regulations to decide what form to take milk in, if you are bottle feeding - BF an advantage as not even airport security can stop you taking your boobs .
Wear "easy" clothes yourself. I once had an interesting moment when security made me take off laced up CAT boots whilst holding a 3mth baby - I was travelling on my own and no-one offered to help.
Change LO as close to boarding as possible and cross fingers that you can get away without changing him/her again - dirty nappies in 'plane loos are not fun!
Definitely feed on take off - mine always went to sleep at that point, which was great.
Take every bit of help / preferential treatment / decent seats / etc offered - it makes everyone else's life easier as well as yours - and take the pushchair to the door of the plane if at all possible - but check where you will get it back at the other end, as it varies by airport.
If you're anything like me, be a lot more paranoid about tickets/passports etc than you would have been pre-baby. I inevitably ended up focused on LO and then panicked when I couldn't find stuff - if you are travelling with your DP make them take charge of all documents - it's just one less thing to worry about.
Lastly - remember that if LO does cry, it sounds a lot louder to you than to anyone else - honestly!