Mark and cut selection

I have Cubase LE 7. I know how to mark a selection and remove it (Cut time = Ctrl + Shift + X), but what is the recommended way to set the start and end point of the selection so that the edits fit the music precisely?

My tracks are audio files imported from a multitrack recorder, and I do not use bar and beat markers, so I cannot select edit points by snapping to the grid. At the moment, I am doing it by trial and error: (1) estimate the start and end points, (2) cut the selection, listen to the result, undo the cut, drag the start and/or end of the selection by a tiny amount, (3) repeat step (2) until I get a tight edit.