Be Impeccable With Your Word
This is a great recommendation. Many people don't realize the power of their words and see the harm that can be caused with speaking carelessly, thoughtlessly or aggressively. Most of us are aware that screaming at someone may be upsetting to them, but subtle little digs at them, or gossip behind their backs, can hurt others more than we realize, and in hurting them, we hurt ourselves. This is an important, but difficult one to follow entirely. It's a great goal to aspire to, though, and a good direction to work toward.
Dont Take Anything Personally
This is good advice for making us feel better, but take it with a grain of salt. While everyone has their biases and there is no such thing as true objectivity, by never taking anything personally, people can really limit their ability to see their own negative patterns and biased thinking, and work on developing more healthy patterns and clear-sighted thinking. As M. Scott Peck says in The Road Less Traveled, "the problem of distinguishing what we are and what we are not responsible for in this life is one of the greatest problems of human existence." Dont give up on the work of distinguishing responsibility, or you end up creating more stress in the long run.
Dont Make Assumptions
However, taking this advice to an extreme may cause people to ignore their intuition about people, or common sense about someone's behavior that's damaging. It can also open people up to manipulation if they train themselves to believe someone's explanation of negative behavior rather than judging the behavior on its own. (For example, not 'assuming' they're being cheated on if their spouse is exhibiting erratic behavior and the classic signs of infidelity, but vehemently denies wrongdoing.) This one is a good suggestion, but should be tempered by inner wisdom and common sense.
Always Do Your Best
I think this is good advice for anyone, and see no down-side to it. This behavior can help people acheive more progress toward their goals, and prevent unecessary feelings of regret.
While sometimes the 'agreements' are oversimplified, in my opinion, this is still a great little book with some heavy ideas. If followed generally (and not fanatically), these suggestions can help you reduce a great amount of stress by helping people avoid thought and behavior patterns that create frustration, blame, hurt feelings and other negative emotions.