1. The tenant(s) details. Full name of each tenant, and the address of the property.
2. Earliest date your landlord can apply to court. The date before which court proceedings cannot begin. The form's note says you must give the minimum notice for the grounds you rely on, and with more than one ground you wait for the longest period. It makes an exception for antisocial behaviour grounds (7A and 14). GOV.UK's Form 3A landlord guidance lists the notice periods.
3. Latest date your landlord can apply to court. Printed on the form: 12 months from the date of service, after which the notice is no longer valid. Not filled in.
4. Landlord's reasons. 4.1 is an optional tick-list of common grounds. 4.2 and 4.3 are mandatory: 4.2 is the full legal wording of each ground from Schedule 2 to the Housing Act 1988, and 4.3 is your explanation of why each ground applies. The form says not to rely on the name of the ground only.
5. Contact details and signature. Signature, whether you are the landlord, agent or licensor, date, name, address, phone and email. For joint landlords, each signs in the additional signatures box or they agree for one to sign for all. The form says that giving an email address means the tenant and the court may use it to serve documents on you.
6. Information for tenants. Printed advice for the tenant; not filled in.