There are many "great" books that deal with your expanding human potential. This is one of the most spiritually powerful texts, packed into 138 pages. Rules simple enough for "ignorant savages" to understand and honour for a few thousand years. This one is the clearest, cleanest and simplest you can read and then put into practice.

1. Be Impeccable With Your Word.
   The broad scope of this concept is to avoid sin against yourself by what you think.  Sinning against the self takes many forms: such as, putting yourself down, gossiping, or putting anybody else down because you don't agree with what they think.  Actions and words need to be consistent as part of being impeccable with yourself.  The other side of the coin is the smoky mirror concept.  Ruiz makes the point that our perceptions of others are merely reflections of ourselves.  Therefore, to put another down or project negative words or energy towards another person, is to lash out at the other person because of our own insecurities.
    
2. Don't Take Anything Personally.
   There is an awful lot of negative energy out there and some of it is directed at us by other people.  If you take it personally and take on the poison of another's words, it becomes a very negative agreement you have with yourself.  What anybody thinks about you, or says about you, is really about them.  Not taking it personally allows you to be in relationship with anyone and not get trapped in their stuff.  This agreement can also pertain to things that we take personally that cause us to go into upset.
    
3. Don't Make Assumptions.
   What we think we understand about what someone says, how someone looks at us, what someone means by what they do, etc, may often not reflect reality at all, and more often than not lead us to think badly of ourselves or of others, and reinforce not being impeccable with our word.
    

4. Always Do Your Best.
   Your "best" is a variable thing from moment to moment.  "When you do your best, you don't give the Judge the opportunity to find you guilty or to blame you.  You can always say, I did my best."  There are no regrets. (p.80)  The other key to doing your best revolves about being in action.  "Action is about living fully.  Inaction is the way that we deny life.  Inaction is sitting in front of the television every day for years because you are afraid to be alive and to take the risk of expressing what you are.  Expressing what you are is taking action.  You can have many great ideas in your head, but what makes the difference is the action.  Without action upon an idea, there will be no manifestation, no results, and no reward."