My baby is now 8 months old and she has been flying at least once a month since she was 5 weeks old, here are my top tips.
Airlines allow families with children to board first - don't. I found that this just adds extra time when you have to sit on the plane and the children are confined. We always board towards the end now and find it much better.
Can't imagine the pain of flying long haul with a baby so completely agree with Froggy that buying an extra seat is a good investment but we manage fine on short haul flights with baby on knee. Remember that even if you get a bassinet, baby can't stay in it when the seat belt sign is on so if there is any turbulance, baby will be on your knee. We flew from London to Hong Kong in January and the seat belt sign was on for three hours mid flight (luckily we were in BC so baby and I could lie down together on the seat).
Take everything you think you will need with you, don't rely on the airline having things.
My baby was exclusively breast fed so we didn't need bottles and we never did purees but remember that if you are taking bottles or pureed baby food you will have to taste it at security. This means your bags will be pulled aside and this can add significant time to the time it takes to pass through security.
Nurse or feed young babies on take off and most importantly landing.
I generally find that check in staff and cabin crew are quite accomodating in moving passengers with infants to empty seats, or at least moving those sitting next to you. On a recent flight the FA asked the two gentlemen sitting next to me and my baby if they would like to move to some empty rows at the back, the chap in the middle moved straight away but the man in the middle said he was fine and just moved to the aisle. A few minutes latter he confided that he would rather sit next to a screaming baby than his 'nightmare' colleague (but she didn't scream).
I have not decided if it is better to get a window or aisle in EC yet. With an aisle seat it is easier to get up if the baby needs a bit of a walk to settle. However, if baby falls asleep and then the other passengers want to get out, you are disturbed. Window seats are also slightly more private for breast feeding. I tend to opt for window seats as I know my baby is pretty settled on flights.