To be peaceful at mind, the first & foremost thing is to be satisfied with what you have at present & try to make harmonious relations with the people all around you. Once you are able to do that then you shall find that you are better off & much peaceful.
The great Bhagwat Gita also teaches us on the same matter & teaches us to be like an Ocean in which all the rivers merges & yet it remains undisturbed. So we too should be calm like an Ocean & though enjoying all things of life & doing our duties should be peaceful just like the Ocean.
In relations, we should also act like shock absorbers where we are not able to retaliate, if some near & dear one says something which is not pleasing to ourselves. We should make understand others about their mistakes by passive rather than active, retaliatory methods. In all cases, we should not lose the peace of our mind by any of our acts & just be Calm like an Ocean. Below is a good verse, "Verse - 70, Chapter Two of Bhagwat Gita" teaching the same thing.
samudram apah pravishanti yadvat
tadvat-kama yam pravishanti sarve
sa shantim-apnoti na kama-kaami” (Gita: Chapter II verse 70)
"Sri Krishna said: O Arjuna, As the waters (of different rivers) enters the Great Ocean, which though full on all sides remains undisturbed, like wise a person who is not disturbed by the incessant flow of desires - can alone achieve peace, and not the man who runs after these desires & strives to satisfy such desires."
Keep your desires in control & think positive; do not hanker after these desires & be just like an Ocean & never lose your peace of mind in any of the circumstances. So always be creative in life by thinking positively as thoughts have the power to change one’s life completely. Be always Positive & always be Happy in Life thereafter.