In terms of supporting genuine relationship, as far as UKBA are concerned they will follow their guidelines to inform their decision.

Firstly, you and your partner have met in person.....
Secondly, you need to very clearly demonstrate that your relationship with your partner is Genuine and Subsisting(click on that link to follow)
Thirdly, you need to convince the ECO that you are only seeking entry to the UK to allow your marriage to take place.

Means you need to convince the ECO that there's a clear intention to actually marry. To be honest, this largely hinges on whether the relationship is believed to be genuine and subsisting.

It's actually impossible to prove an intention, and likewise no concrete evidence can be provided. Even receipts for a wedding dress and rings etc do not prove an intention. However, they can help to build a belief with the ECO

I think you've surely already made some tentative plans and had some discussions together for the future wedding. Any evidence at all, however small, to show that wedding arrangements are in hand will all help.
How about any e-mails, texts or facebook messages that specifically mention wedding plans, especially in connection with:-
- Where and when
- Rings, dress, cake, catering, reception
- Guests, invitations
- Any quotations relating to wedding arrangements (just demonstrates that the couple have some intention)
- Honeymoon

If UKVI believe the relationship is genuine then they usually believe a marriage will take place given reasonable evidence.

Have your sponsor write a good supporting letter for submission with your application.
Briefly outline how and where the relationship started and how you met, how it developed, how long you have been together, how you have maintained contact, important events, meetings between yourselves, things you did together and plans you have made for living in the UK (specifically, why you are opting to live in the UK.
Mention the times you met face-to-face. Include boarding passes,hotel receipts etc. Have some photos with family members and also as a couple showing some things you did together.
Confirm your feelings for each other, why you want to marry, plans for the future and where you will live and how you will support yourselves.
Keep it as simple as possible and above all be honest about everything.

Why not consider including a supporting letter from both sets of parents/siblings etc acknowledging the engagement and wedding and welcoming you both into the family.

These are just some ideas for you to build on. Hope it helps