Either party can end a month to month agreement by giving the other party twenty day's notice. However, the notice has to be given within ten days of when the rent is paid to be effective for the last day of the month.
If you pay/collect rent on the first, a notice delivered by the tenth is sufficient to end the tenancy on the last day of the month. If rent is due on some other day, adjust accordingly.
20-day notices are "no fault". The tenancy is over and no reason has to be given.