Wa alaykum assalam,
This is something someone advised to me, and it really helped me with focusing on my salah.
If you haven't already, then try to memorise the english translations of everything you recite in salah if you don't know Arabic already. I found that when I actually understood what I was saying, and the power and beauty of the supplications you are making, concentration becomes so much easier.
I once read that the more you become closer to Allah swt, the more the shaytaan tries to lead you astray with his whispers, because it's a defeat for him when someone is on the straight path. So when you read salah, he will try to distract you even more, and to ignore those whispers you need a really strong focus on salah, and why you are doing it, and Who you are praying to.
This is a lifetime struggle, may Allah swt allow us all to attain ihsan and excellence in our worship. Ameen.