The feeling of valuableness comes from finding something of value within oneself. It has to be something real — that one can experience or put to use immediately within oneself and not just a conceptual idea.
This will ensure that it is always there, a concept loses lustre and needs to be replenished over and over again.
Even the man who has not attained enlightenment ( which is almost everybody ) has something of value within himself. If he has not realized it, he needs to keep searching within himself, when it arises, it will not feel like something he had to convince himself of but of just sheer value as is. It might be talent, who he is as a person, a gift etc. it has to be something within himself that arises naturally — without him having to convince himself. Convincing oneself is false — such as affirmations.
Once one finds it, it will be a center within themselves that can be anchor for everything else. He can built everything else around it, because now he has found a solid foundation within himself, an immovable point within himself.
The way he is, walks and interacts with people will be a reflection of this new found center. He will exude a confidence that the self help guru often preaches about, and he will do it not out of learned behavior but as an effect of this new realization. This will be the portal through which the universe will flow an abundance to his life, it will be the space from which doors are opened for him, it is because of this that he will never lack.