1-Whatever invalidates purification also invalidates prayer.

2-Loud laughter.

3-Deliberate normal speech for any purpose other than that of the prayer itself.

4-Deliberate exposure of one’s Awrah.

5-Turning one’s back towards the qiblah.

6-Contact with impurity.

7-Deliberately omitting. 

8-Doing any of several things that are not related to the prayer.

9-Leaning against something without any legitimate reason.

10-Deliberately adding a rukn that involves an action.

11-Deliberately changing the order of rukns.

12-Deliberately saying Assalamu 'alaikum before prayer is finished.

13-Deliberately changing the meaning when reciting al-Fatihah, as its recitation is a rukn.