Is there any preparation necessary before the colonoscopy?

Yes. There are many variations of "the prep", but in general you will need to restrict your diet to clear liquids the day before the procedure, and drink a prescribed preparation to wash out your colon the evening before and possibly the morning of the procedure. There may be other instructions for the avoidance of certain foods (seeds) for a few days in advance.
Yes. And most physicians / centers have a specific routine of dietary changes with laxatives, so it is ver important to follow the instructions given to you. One of the most important factors for a quality colonoscopy is an excellent prep.
Prep med and diet. There are several commercially available prescription bowel preps that your endoscopist can order prior to th exam. There is usually a modification of one's diet the day before the procedure. I prefer that the bowel prep results look like "mountain dew" for the best exam.