This sort of question hits close to home for me, as I used to be highly judgmental, and still am to a certain degree. PM and Mark's writing has helped me a lot with this.
1. I totally agree with self-acceptance and being judgmental of others being related. To me they are each a barometer of the other. If someone says highly judgmental stuff all the time, I'm guessing they don't like themselves much. Similarly, if someone doesn't seem to like themselves much, I'm guessing they think a lot of judgmental thoughts. Of course making this assumption can be judgmental in itself, so I try not to be too quick with it
2. Like self-acceptance, being less judgmental is something that comes slowly over time, although it often comes from those mini-emphanies you have, like when you see something in a different light for the first time and realise that co-worker you don't like is trying hard to be a good guy, or that that unpolite attitude your friend has you also display at times.
3. There are a number of things you can intellectually believe are true at first, and then work to emotionally believe and integrate. The ones you've mentioned are good, and there are many more. My personal favourite is: 'remember that everyone is doing their best to be a good person and to make themselves happy'. I used to believe almost the exact opposite of this; I would think everyone was so lazy when it came to pursuing what they love, or that they didn't care about being a good person as much as me, or that they were totally illogical and I was the only one who seemed to see things straight.
4. What helped me change that was a number of things. Firstly, the self-hatred from which it came from just became too exhausting, and I was ready to give it up. A lot of people take longer to get to that place though, so I was lucky. Secondly, really making a conscious effort as often as I could muster the strength to. Some days you just don't want to tell yourself that there's more to the story than meets the eye; you just want to think your hateful thoughts and feel better about yourself. That's ok, we don't win all our battles. You just keep trying. Thirdly, a number of resources helped me, which I recommend you read one by one.
A) This is Water- A speech by David Foster Wallace: http://postmasculine.com/this-is-water
Probably no one single thing has helped me more than this speech. All of DFW's work has made me think deeper about life, to appreciate its complexities, and to withhold judgment, but this is on another level. Check out Mark's post on it to get an insight as to why it's so deep: http://postmasculine.com/why-self-help-sucks
I read the speech a while before Mark posted it on the blog, but this took it to another level for me.
B) A number of articles from Postmasculine.com, in particular http://postmasculine.com/you-are-not-a-victim
, and many many more.
C) The Zen Habits blog at http://zenhabits.net/
- Leo Baubata. Encourages you to look at life openly, to live simply, and to focus on that which really will make you happy. Probably the greatest influence a blog had/has on me outside of Mark's blog.
There's more, but I won't list it all here. As I became more open to being less judgmental, and made it a priority in my life, more and more resources started showing up that I found relevant. I'm sure the same will happen to you.
Finally, my journey from finding PUA to eventually leaving it, was a huge thing for me. I was highly indoctrinated for a long time with PUA thinking, and leaving it has meant my beliefs and understanding of the world have changed drastically. I went from thinking I knew everything and yet I felt incredibly confused and uncertain. After I left it, and began to normalise myself, I realised that I knew very little, and yet I feel far more sure about myself and the world than I ever did before. PUA messed me up badly for a while, but there's no way I would have the ability to reserve judgment that I have now without it. I'm sure there are areas of your life that can do the same for you.