A person should be mindful to wash his hands with mayim achronim before the Birkat HaMazon, Grace after the Meal. One should place just a small amount of water on the tips of one’s fingers so that he doesn’t become susceptible to the Sitra Achra. I have heard of a wondrous incident that happened to the pious Rabbi Yehudah Havillyo with this practice.

Also, one should be sure to recite the blessing after the meal immediately afterwards; one should not interrupt even for learning except to recite four verses: “I bless Adonai at all times; praise of Him is ever in my mouth.” (Ps.34:2) “The sum of the matter, when all is said and done: revere God and observe His commandments! For this applies to all mankind.” (Ecc 12:13) My mouth shall utter the praise of Adonai and all flesh shall bless His holy name forever and ever. (Ps. 145:21) And he said to me, “This is the table that stands before Adonai.” (Ez. 41:2) and Psalm 67 - “May God be gracious to us and bless us…” 96

One must be careful to have the intention to fulfill the positive commandment of the Torah, “You shall eat, and be satisfied and bless…” (Deut. 8:10) If there are three people present then one should begin with a zimun.97 when a minimum of three adult Jewish males eat bread as part of a meal together they are obligated to form a mezuman (a "prepared gathering") with the addition of a few extra opening words whereby one man "invites" the others to join him in birkat hamazon. (This invitation is called a zimmun). When those present at the meal form a minyan (a quorum of ten adult Jewish men) there are further additions to the invitation. The zimmun is sometimes mistakenly referred to as a mezuman. (halachapedia)