You can only increase rents every 12 months and you have to give 90 days notice. So if you want to increase your rent for September 1, you will have to serve notice by June 2. You can only increase the rent up to the maximum guideline percentage. When calculating that, you are not allowed to round up, only rounding down is permissible. Also be aware you cannot backtrack for missed rent increases, i.e. if you did not increase your rent in 2019 you cannot catch up on that, but only do the increase as per the 2020 guideline in 2020.
The guideline percentage is announced each year by August 31, and will then apply for the following year. For 2020 the percentage was 2.2%, and it was published in mid 2019. For 2021 the guideline amount has been set to zero due to Covid. There's only a defined number of exemptions to that zero increase rule (see Bill 204). Increases will be possible again after December 31, 2021. Once again the guideline percentage will be announced in either July or August this year. If you intend to increase the rent for January 1, 2020 to keep in mind the 90 day notice period. Make sure you serve your tenant by the end of September 2021, mark your calendar!
Servicing the N1 can be done either in person, into the tenants mailbox, under the door or by fax. The LTB / Tribunals Ontario website has a "certificate of service" that may help you in this regard. Service by email is possible with the written permission of the tenant. There's a consent form available from LTB for this purpose.
While the form itself is great, I find it doesn't look very friendly in the hands of the tenant. To avoid this, I write a personal letter, that includes all the content of Form N1, but looks a bit less like a parking ticket. On a side note, Forms N2, N3 and N10 are also rent increase forms. They apply in special situations.
Download forms here: https://tribunalsontario.ca/ltb/forms/#landlord-forms
These resources may prove helpful in filling out Form N1 and give deeper insights:
https://www.ontario.ca/page/residential-rent-increases#section-0
https://landlordselfhelp.com/podcast/n1-notice-of-rent-increase/