The venerable Sam Bain has written a very helpful blog about giving and receiving notes here. I agree very much with what he's written, and can add my tuppence to anyone who cares to listen.
It's worth thinking about why receiving notes is so painful. There are a few reasons that spring to mind. The first is that writing a script is an emotional process. The script is like an offspring that bears one's own DNA. Your characters are almost like children. It's impossible to receive criticism of one's offspring and not take it personally. Any attack on them stings.
The second is a more pragmatic source of pain. When the notes get going, and you realise there are problems to be fixed, you know that this is going to mean work. Cutting, editing, losing your favourite jokes and scenes, and thinking of something new, original, clever, funny and suitable to go in their place. This will take hours. And you know that these new scenes and lines in themselves will be subject to further notes.
These two things lead to grumpiness - and can easily tip over into resentment, especially if you're not impressed with the script editor's credentials. I personally find it hard to take notes from producers and script editors who haven't made any comedies that I really like or respect. (It is worth pointing out that you need to be careful not to believe every note you are given.) But in general, one needs to just suck it up and judge each note on its merit, not on the CV of the note-giver, and consider if there's anything in it. There usually is. Even the silliest or most spiteful criticism has a grain of truth at the centre. Most notes are not silly or spiteful, so listening to them really shouldn't be all that hard.
So what I have to do is remember one thing - that every rewrite makes the script better. Draft 1 is always a messy over-written jumble. The notes help draft 2 to be a more focussed bit of writing that still needs a good kicking. Draft 3 should be in decent shape, but still needs cutting down and punching up, so that Draft 4 is at least readable by actors. And then you do Draft 5.
It's easy to take your foot of the gas half-way through Draft 3 or 6, and start ignoring the notes, or assuming your cast will 'do something with that bit'. At that point, you need to remember a feeling you'll have in a few weeks time when the script is recorded in front of an audience, or broadcast on television - it's a little stab of disappointment of seeing your cast perform some lines of yours that you know in your heart of hearts aren't quite right and could be better. Remember that feeling. Take the notes. Put the hours in. Do it again. And again. And again. And again. If you don't, the biggest loser will be you.