Not he is chaste in whom shameful thoughts stop in time of struggle, work and endeavor, but he who by the trueness of his heart makes chaste the vision of his mind not letting it stretch out towards unseemly thoughts.
The more wood you pile on a fire the more heat you get, and thus it is with God - the more you think on Him the more you are fired with love and fervor towards Him. He who loves the Lord is always mindful of Him, and remembrance of God begets prayer.
You ask for some way of completely eradicating irritability. The inclination to irritability is given us to use against sin, and we were never meant to use it against our fellow men. When we do, we act contrary to our true nature.
We ought not to grieve or become irritated at anything because, by frequent vexation and irritability, we form the morally and physically very injurious habit of irritability, whilst by bearing opposition with equanimity we form the good and useful habit of enduring everything calmly and patiently.
If you wish that God should speedily give you hearty faith in prayer, strive with all your heart to speak and to do everything in regard to other people sincerely, and never be deceitful in your dealings with them. If you are straightforward and truthful with others, then God will give you straightforwardness and sincere faith also in reference to Himself.