Things that are Makruh to Do in Salah

Actions that ruin the concentration and khushu (reverence) of prayer, preventing one from focusing and worshipping Allah (swt) in complete devotion, respect and obedience during prayer are disliked. While it does not invalidate the salah, these actions decrease the reward and joy one gains and are termed makruh: disliked and disapproved.  Abandoning a wajib or sunnah act is considered makruh as well.

Some of the makruh acts are to fondle unnecessarily with ones clothes and fingers, or cracking the knuckles in salah; to yawn and stretch; to turn the head and eyes left and right; to perform salah while one needs to use the toilet; to perform salah with a small amount of filth which does not invalidate the prayer despite being able to clean it; and to perform it in places and situations which affect the spiritual state of the person.