The glass on both the outside and the inside will need to be cleaned using a mild water and detergent mixture. The solution should be weak enough that it is not able to make bubbles if agitated. Use a soft cloth to gently scrub the glass from top to bottom. Use a dry cloth or newspaper to thoroughly dry the doors and to prevent streaking. The newspaper is effective at absorbing any moisture. It will also remove the scum layer which may have stayed on the glass. The end result should be a sparkling high gloss.
If you find that the glass is not completely clean and free from smudges after these steps, especially when smears and fingerprints have been left behind, you are going to require something that is a bit more astringent. A concentrated solution of white-vinegar and a little bit of water applied using a leather chamois should be an effective solution to remove all the marks. Ensure that you dry the glass using newspaper which should return your glass sliding doors to a shiny full gleam.
If you find after all these steps that there are still marks left behind, make sure you avoid trying to remove them with a sharp object such as razor blades. This is a procedure which is only suitable for standard glass. As a last resort use neat vinegar to try and rub away the marks with a clean kitchen towel. If this fails to remove the marks, then it is more than likely that the mark is actually a scratch which has been etched in the glass.