When looking for guidance on your specific situation, best option is to employ the services of registered migration agent. When you submit, you will have peace of mind that your application crossed all the Ts and dotted all the Is. They are quite costly - at least there's a price for peace of mind.
A Case Officer is looking evidence that your relationship is genuine. This generally takes the form of:
- Photos of the applicant and the sponsor (just both of you)
- Photos of the applicant and the sponsor with friends/family
- Photos from an engagement party or from the day of the proposal
- Proof of holidays you went on together (etickets for both of you)
- Tickets/receipts from events that you went to together (cinema, concerts, receipts for dinner, name cards from someone's wedding reception)
- Etickets when the applicant visited the sponsor in Australia
- Etickets when the sponsor visited the applicant in their residing country
- Statements from any accounts which is in both of your names (perhaps a joint bank account was opened when the applicant visited the sponsor?)
- Bills for each of you showing that you lived at the same address (one bill with both names on it is very useful)
- Correspondance during periods of separation (WhatsApp log, Viber log, Skype log, Phone calls, etc)
Some of the above may not apply to your situation. I assume you are the Sponsor?
Statutory declarations support evidence of a genuine relationship. I submitted 2 as part of my PMV. Statements from non Australian/New Zealand PR/Citizens don't hold much weight.
Additionally, my sponsor did the following:
- obtained a 'Notice of Intended Marriage' from the celebrant
- obtained a signed letter from the celebrant
- obtained a signed letter from the priest
I haven't included the standard stuff (passport, birth certificate, police checks, etc), but the above lists should give you a general idea of what you need to achieve.