Imam Al-Ghazali's: Inner Dimensions of Islamic Worship
This is a book comprised of sections from Imam Ghazalis celebrated work Ihya Uloom id Deen. Imam Ghazali goes through the various ibadah we must do, salah, zakat, sawm, hajj/umrah and amongst other things he expounds upon the importance of khushoo in them, of having presense of the heart in worship and how to try and obtain it. It's a really important topic, and this would a useful read for anybody and everybody, so buy it inshaAllah.
I enclose my notes from lessons studying the text under the tutelage of Shaykh Muhammad Al-Yaqoubi. As ever, they aren't exhaustive, there is a section missing toward the end which I left for someone else to type up, but haven't been able to obtain since. Read my disclaimer ..and keep me in your dua's!