The order of the lines in the cron is not significant. Lines can be entered anywhere in the file, but it is sensible to group related lines together (for example, all daily jobs).
Any line in the cron beginning with “#” is treated as a comment, and is not executed as a command. Liberal commenting of the root cron file will can help others understand the function of each line.
Be careful not to add blank lines to improve the readability of your file. This can result in problems to your scheduled cron jobs. Instead, precede blank lines with the pound symbol so that the rest of the line will not be interpreted.
The following diagram shows a typical cron file: