First Mistake 

Reciting Surah Surat al-Fatiha very fast without pausing. 

 The Prophet (ﷺ) used to pause after each verse of this surah. (Abu Dawood).

Second Mistake 

Sticking the arms to the sides of the body, in rukoo’ or
sujood, and sticking the belly to the thighs in sujood.

The Messenger of Allah (ﷺ) said: ‘Let not one of you support himself
 on his forearms (in sujood) like the dog. Let him rest on his palms
 and keep his elbows away from his body.’ (Sahih Muslim). The
 Messenger of Allah (ﷺ) used to keep his arms away from his body
 during rukoo’ and sujood that the whiteness of his armpits could be
 seen (Sahih Muslim).

Third Mistake 

Gazing up during the prayer. 

We can lose our concentration in prayer. We are commanded to lower our
 gaze, and look at the point at which the head rests during sujood. The
 Prophet (ﷺ) warned: ‘Let those who raise their gaze up during prayer
 stop doing so, or else their sights would not return to them. i.e.
 lose their eyesight].’ (Muslim).

Fourth Mistake 

Resting only the tip of the head on the floor during sujood.

The Prophet (ﷺ) said: ‘I am commanded to prostrate on seven bones
 the forehead and the nose, the two hands [palms], the two knees, and
 the two feet.’ (Sahih Muslim). When we apply the above command, it requires resting the forehead and the nose on the ground during sujood.

Fifth Mistake 

We hasten to go to the prayer or mosque and we end up losing tranquillity and calmness in prayer. 

The Messenger of Allah (ﷺ) saw a man who did not complete his rukoo’
 [bowing], and made a very short sujood [prostration]; he (ﷺ) said:
 ‘If this man dies while praying in this manner, he would die upholding
 a religion other than the religion of Muhammad.’ Abu Hurairah (RA)
 said:

‘My beloved friend, Muhammad (ﷺ) forbade me to perform postures of
 prayer copying the picking of a rooster; (signifying fast performance
 of prayer), moving eyes around like a fox and the sitting like monkeys
 (i.e. to sit on thighs).’ (Imam Ahmad & at-Tayalisi) The Messenger of
 Allah (ﷺ) said: ‘ The worst thief is the one who steals from his own
 prayer.’ People asked, ‘Messenger of Allah! How could one steal from
 his own prayer?’ He(ﷺ) said: ‘By not completing its rukoo’ and
 sujood.’ (At Tabarani & al-Hakim).

To complete rukoo’ is to stay in that posture long enough to recite
 ‘Subhana rabbiyal Adtheem’ three times, SLOWLY, and ‘Subhana
 rabbiyal-a’ala’ three times, SLOWLY, in sujood. He (ﷺ) also
 announced: ‘He who does not complete his rukoo’ and sujood, his prayer
 is void.’ (Abu Dawood & others).

Sixth Mistake 

Counting tasbeeh with left hand and  on masbahah.

The Prophet (ﷺ) used to count tasbeeh on the fingers of his right
 hand after salah. Ibn Qudamah (RA) said: ‘ The Messenger of Allah
 (ﷺ) used his right hand for tasbeeh.’ (Abu Dawood). 

The above hadith clearly shows that Prophet (ﷺ) used only his right hand to count tasbeeh. 

To count tasbeeh on rosary beads or masbahah is bidah. Unfortunately, this practice has become wide speared among the Muslims.  It was never done by the Prophet (ﷺ) neither by his companions. 

Shaykh al-Islam Ibn Taymiyah said in al-Fatawa (22/187): “Some of them might show off by putting their prayer-mats over their shoulders and carrying their masbahahs in their hands, making them symbols of religion and prayer. 

Al-Shaykh Muhammad Nasir al-Deen al-Albani said in Al-Silsilat al-Da’eefah (1/110)

He said “If there is only one bad thing about the masbahah, which is that it takes the place of the Sunnah of counting on the fingers, even though all are agreed that counting on the fingers is preferable, then that is bad enough. How rarely I see people counting their tasbeeh on their fingers!

Seventh Mistake 

To Cross in front of a praying person.

The Messenger of Allah (ﷺ) warned: ‘Were the one who crosses in
 front of a praying person to know the consequences of doing so, he
 would have waited for forty better than to cross in front of him.’
 (Sahih Bukhari and Muslim). *

The forty in the tradition may be days
 months or even years. 

Reference

Author not mentioned (11-11-1998). 3009: Ruling on using the masbahah (prayer beads)

Retrieved from: https://islamqa.info/en/answers/3009/ruling-on-using-the-masbahah-prayer-beads