Its important to make sure that your materials are in order before beginning anything. This means laying out your magnets, making sure you have enough, and measuring your space underneath your cabinet.
I laid out my magnets on my spice jars. The tops are metal (steel?) so the magnets stick, but you want to make sure that your magnets are all pointing the same direction.
I also made a quick and dirty template for drilling my holes by tracing the bottles on a piece of cardboard and stabbing it with a knife.