According to Sahih Muslim you shouldn't do following things while praying:
a.. Clothes having designs and markings on them are distracting and should be avoided ( refer Sahih Muslim book 4, hadith 1131-1133 )
b. The Prophet commanded the believer that while praying 'he should not spit in front of him, for Allah is in front of him when he is engaged in prayer' ( refer Sahih Muslim book 4 , hadith 1116 ). According to another tradition, he 'forbade spitting on the right side or in front, but it is permissible to spit on the left side or under the left foot' ( refer Sahih Muslim book 4 , hadith 1118 ).
c. To eat onion or garlic is not harm (forbidden), but Muhammad found their odors 'repugnant' (refer Sahih Muslim book 4 , hadith 1149) and therefore forbade coming to the mosque after eating them, 'for the angels are harmed by the same things as men' ( refer Sahih Muslim book 4 , hadith1145 ) .