In Arthur Miller's play Death of a Salesman Willy Loman certainly has a number of axioms or tenets by which he intends, or at least tries, to live his life. These come in the form of sayings or, like your question proposes, "slogans", that appear quite real to Willy. Unfortunately, that is all they are: All talk.
One of the things that Willy says a lot is that he is "The New England Man" and that he is "Vital in New England".This is the way that Willy describes himself to Linda to make her believe that he is a quite necessary man for his insurance company. Saying this not only makes him feel special, but he actually believes it. He knows that his time is coming to an end, but Willy is the type of person who lives by what he says, and not by what he does.
Another thing Willy says a lot has to do with "being liked". In Act I, and all throughout his life raising the boys, he has always said
Be liked and you shall never want.
He even tells Biff that Bernard, Biff's well-raised friend from school, will not make it too far in life regardless of being smart because
He's liked, but not well-liked.
All that is quite ridiculous anyways because we can tell from the surface that Willy's imperious attitude and his shameless exposure of his ideas make him a very hard-to-like person. One is not surprised that, throughout the entire play, he can only count with one friend and that is Charley, who is Bernard's father. Charley goes out of his way and gives Willy money just to save him from the shame of not being able to provide for the family. Charley is also the only person who attends Willy's funeral. Having nobody at your funeral and being ignored through life is the epitome of NOT being well-liked. Certainly Willy cannot live by the tenets that he proposes for everybody else.
One very important thing Willy says to Biff is
I am not a dime a dozen! I am Willy Loman, and you are Biff Loman!
This shows how deeply Willy believes in his own fantasy of being a vital, important, and powerful man. His idea is deeply ingrained in both his heart and soul, and he still tries to get Biff to believe in it. However, this is also the very moment when we realize that Biff has finally awoken from Willy's dream.
Therefore, most of Willy's sayings or tenets for life are created out of the idea that he has acquired his American Dream. We, as the audience know, however, that all of these sayings are merely a part of Willy's imagination, and maybe they are the only thing that Willy has to himself to "keep going".