Take on love of every Jew before you pray
Before davening, the Arizal teaches us to take on the mitzvah of loving every Jew, so that our prayer rises joined with the prayer of all Israel.
The Arizal taught that a person who has sat down in shul should, before he begins to pray Shacharis at all, accept upon himself the mitzvah of loving his fellow as himself, and intend to love every Jew as his own soul. The reason is that prayer is not a private errand. Through this acceptance, a person's prayer rises as one joined with all of Yisroel, and can ascend and bear fruit. This short declaration, which begins with the words Hareini mekabel alai, is printed at the start of many siddurim, and countless Jews recite it each morning before davening.
Source: Pri Etz Chaim, Sha'ar Olam HaAsiyah 1
Tomorrow morning, before the first word of davening, pause for ten seconds and say, in whatever language you like, that you accept upon yourself to love every Jew as yourself. Then bring to mind one specific person you find difficult and wish them something good. If you pray with others, look at the person next to you and mean it. You are not asked to feel a rush of emotion, only to open the door. Over time the habit softens the heart and changes how you treat people all day.