Some Cayce quotes to get you started:
Yet ye are seeking in this to know what is the Destiny of the Mind. What has been set? Where is thy Destiny? It is in what one does about that one knows that one becomes in oneself. For it is oneself from one's portion or activity of that first movement of Mind from the spiritual aspect or from the material aspect. (262-78)
These in their various manners present the correct interpretation, then, of the Destiny of the Mind. Mind is, as has been given, both physical and spiritual; is amenable to laws that govern same in its phase of manifestation. Mind is the motivative influence in expression as to the growth in which the inward self would make for its expressions in materiality or in matter. What meaneth, then, those that spoke as given, "As a man thinketh so is he"? So does the growth become. For in the material things, as we shall find as respecting the Destiny of the Body, as a man eateth so is he also - the physical man. As a man thinketh so is he also; destined that that which is the growth of those influences in the experience of the individual for its accomplishing, its fulfilling that purpose for which it came into being.
Then the question, naturally, is asked: Is the Destiny of a Mind set at the time of its birth into materiality? as to what it will think, as to what its environs will be, as to the length of its period of expression in the earth? Is it destined to lose a tooth on a certain day, a hair on a certain day, an arm, or this or that experience. These are in those signs that have been indicated, that as ye ARE, as ye were, so will ye be by or through that which has been accomplished in the experience of the body, of the mind, of the soul; that it, the soul (the only living portion of same), might be one. It is destined that it will pass through that experience necessary to give it, the soul, the greater opportunity for its becoming one with that purpose for which it came into being. For God hath not willed that any soul should perish but with each temptation hath prepared a way, a means of escape. This, then, would indicate that as the soul, or as the man, or as the mind works at in its thinking it becomes. (262-79)
Keep thine own self from condemning in others that thou doest in thine own mind or heart, for that one sows in the mind is reaped in the action of another toward self; or self measures self by the action of self's mind builded toward that of another. So make thine own paths straight. (5459-2)
Mind is the Builder. This is ever indicated in the experiences of individuals who hold to or build resentments, or build differences in any way or manner as related to activities or relationships of the body. For these become a barrier, that may make for destructive forces in the physical as well as the mental and the spiritual attitudes. As we find, the physical conditions oft make for irritations - by the differentiation in relationships of individuals to self as well as to others. (1603-2)
(Q) Why is it difficult for me to remember?
(A) It isn't difficult! It's rather trained in self to forget! See the differentiation between forgetting and remembering, is – memory is the exercising of the inner self as related to thought. To acknowledge that the memory is poor, is to say you don't think much! The forgetting is to say that the thought becomes self-centered, for memory is thought – even as thought is memory, brought to the forefront by the association of ideas. (69-2)
What one thinks continually, they become; what one cherishes in their heart and mind they make a part of the pulsation of their heart, through their own blood cells, and build in their own physical, that which its spirit and soul must feed upon, and that with which it will be possessed, when it passes into the realm for which the other experiences of what it has gained here in the physical plane, must be used. (3744-5)