My question is related to the expression used in the translation of the Qur'an. Many times the expression "We" is Used for Allah (I suppose) e.g. Surah 97 Ayah 1 and Surah 7 verse 7 and so on. Please explain what does this mean. How to achieve tranquility and reverence in Salat?

Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

Allah mentions in several verses that He has revealed His Book in a clear and intelligible Arabic language. Allah Says (interpretation of meaning): {And truly, this (the Qur'ân) is a revelation from the Lord of the 'Alamîn (mankind, Jinns and all that exists), Which the trustworthy Rûh [Jibrael (Gabriel)] has brought down; Upon your heart (O Muhammad SAW) that you may be (one) of the warners, In the plain Arabic language.} [26: 192-195]. Allah also Says (interpretation of meaning): {And thus We have sent it down as a Qur'ân in Arabic, …} [20: 113].
Having established, this know dear brother that the Arabic language uses the plural pronoun "Nahnu" (We) for the group as well as the individual, if he wants to glorify himself. This is the case in the Qur'anic style. So, Allah, The Exalted, The Most High, The Glorious uses "We" to express His glorification. Allah Says (interpretation of meaning) for example: {We relate unto you (Muhammad SAW) the best of stories …} [12: 3].
As for how to achieve tranquility and show reverence in the prayer, it is through resorting to Allah and seeking refuge with Him asking Him to help you get this high quality of good believers. Here are some ways that can help you reach this quality. First, reading Qur'an while concentrating on its meanings. Try to make your mind fully occupied by the Qur'an while you are reading it. Moreover, you should think about your Lord and that you are in front of Him and that He is watching you, following all your acts minutely not leaving any detail.
Another yet very important thing is to leave committing sins, as sins can constitute a bad layer on the heart preventing it from being good and ready for tranquility.
Allah knows best.