I've had a colonoscopy twice and the only advice I would give you is that if you are given a choice between sedation and Entonox (gas and air), then go for the sedation. I had that first time (wasn't given the choice), and I was zoned out, perfectly conscious, but in a sort of blissful dreamlike state, with no sense of discomfort at all. In fact, I don't recall any sensation as the procedure was carried out.
But the second time I opted for Entonox, on the strength of the advice from the staff that recovery would be quicker, that I would be able to drive immediately etc. etc. For me, though, it wasn't enough, and the procedure was quite uncomfortable.
I was told that the sedation included painkillers, but the Entonox did not. To be honest, if you have the sedation rubysong, you won't be aware of anything much going on. And if you have someone to take you home and be with you until the effects wear off (not long). then I'd definitely go for this.
As for the prep, just stay near a toilet! I spent the day upstairs in bed with my Kindle and iPad, because we don't have a downstairs toilet .
Good luck