A person should wash his or her hands before davening Minchah and Maariv (with a cup is somewhat preferable). If there is a break between Shacharis and Mussaf (kiddush, or some type of activity), one must wash before Mussaf as well. (Washing for Shacharis is a given, of
course, and even requires a b’racha).
Chofetz Chaim writes that if one speaks loshon hora or other forbidden speech in a Shul or a Beis Medrash, then besides the inherent issur of the forbidden speech, he or she is showing that they have not really internalized the idea that HKBH’s presence is in these places in an intense way, and thus they also violate the prohibition of mora mikdash, awe of Holy Places.