Dear brother
Assalam. Well, you first need to fill out the application perfectly. Then you need following documents:
1) Passport size photos, yours- 2 and partner's- 1.
2) Passports of your partner and your.
3) Biometric residence permit- Yours
4) Marriage certificate
5) Bank statements
6) Pay slips
7) Life in the UK test letter
8) 6 letters to you and your partner from 3 or more different sources in last 2 years.
9) Tenancy agreement
10) Bank savings statement
11) Tax credit letters
12) Work contract letters (your and your partners)
You may add more documents according to your circumstances.
I have just posted my application by Special delivery to Home office. I also included an envelope with special delivery stamps to get the documents back from the office.
I will surely update you about my application.
Hope this helps.
Regards
Maruf