Concentration in Salaah (Khushoo' and Khudhoo')

Q: If I prayed my salaah and I felt a lack of khushoo and felt as though my mind was diverted by dunya matters, should/can I repeat the salaah?

Q: While performing salaah, I am overcome by stray thoughts. When I realise that I am in salaah, I divert my mind from these thoughts and try to concentrate. How can I rectify this problem?

Q: How can I stop stray thoughts from coming into my mind while performing salaah? What is the best way to concentrate in salaah?

Q: Tell me things in order to make myself become alright in prayers.

Q: In my namaz whenever something comes in my mind, even if I try to regain my concentration I forget what I read, in which rakaat I am and many other similar things. What should I do? 

Q: I would like to know while reading namaaz, can you have a cd playing in the background (recitation of Surah Yaseen). Because we have learnt that when reading saalah you have to give you full concentration.

Q: I have read that during namaz one should focus on the words being recited. But if one does not know the meaning of those words, how is it possible to "focus" on those words? Should we imagine that we are actually "seeing" those words written somewhere, similar to focusing on text written in a book.