12:1 The Navi tells us (Amos 4:12), “Prepare to meet your God,” meaning that one who is going to stand before God in prayer should prepare himself by dressing properly, like he would before meeting with a government official. Even when davening alone at home, one should dress in such clothes. If one is in a place where people would not normally go out without a belt, he should not daven without a belt. (Mishnah Brurah 91:12 cites the practice to wear a hat on top of one’s yarmulke.)
12:2 It’s a good idea to give charity (“tzedaka”) before praying, based on Psalms 17:15, “I will see Your face with righteousness” (the word for righteousness, tzedek, is from the same source as tzedaka). Before praying, a person should accept upon himself the mitzvah to love our neighbors as ourselves (Lev. 19:18). If he does this, he chooses to unify himself with other Jews. Because of this, their prayers might likewise be united, and unified prayers are more desirable prayers.