Descartes wanted to build a system of irrefutable knowledge off of his "I think, therefore I am" observation: the idea that we can discern how things are by reflecting on mind, matter, and the nature of God. The intellect, not the senses, was what he supposed was most reliable.

The general consensus as I understand it is that by the Third Meditation, the project had failed: at that point he was appealing to God and infallible personal sense of clear and distinct personal perception (by virtue of God's necessary nature as a non-deceiver).

Starting with consciousness leaves one pretty much in the same situation as Descartes; at the very least, one should spell out how one is going to proceed in a fruitful way.