run cron at 00:00, on day 1 of the month

0	1	*	*
				Day of the week (0 - 7) [Both 0 and 7 represent Sunday]
			Month (1 - 12)
		Day of the month (1 - 31)
	Hour (0 - 23)
Minute (0 - 59)

Cron explainer

Asterisk (*) means "any" or "every".
For example, an asterisk in the minute field would mean "every minute".
Comma (,) can be used to specify multiple values.
For example, "1,15" in the minute field would mean "at 1 and 15 minutes past the hour".
Hyphen (-) defines a range.
For example, "1-5" in the hour field would indicate "every hour between 1am and 5am".
Slash (/) specifies increments.
For example, "*/15" in the minute field would indicate "every 15 minutes".

To learn more about the cron job syntax, see the cron job schedule syntax guide, and to get some help troubleshooting your cron jobs, see the guide for common cron job errors.