Hello Raghav!, I am Aaryan a fellow GSoC contributor in this Organization. Mailman community would love to accept contributions from a guy having a skill like yours! Posting the important links
This is the org's link for GSoD https://wiki.list.org/DEV/SeasonOfDocs2019
This the google's guide for GSoD https://developers.google.com/season-of-docs/ https://developers.google.com/season-of-docs/docs/participants/ https://developers.google.com/season-of-docs/docs/timeline
Apart from building a solid proposal, I would like to know, what exactly should I do in this period to increase my chances of selection. I am looking forward to be a long term contributor, both in terms of code and documentation for GNU Mailman organisation. Looking forward to your response.
I would say pick up a project ( or offer a new one ) go through it completely by asking relevant questions in the mailing list so that for the proposal the whole workflow should be concrete and exhaustive.
You can post any doubt ( project specific or in general regarding Mailman ) in this list. Cheers!