If you already know what you want to work on, then share your planned approach on the discussion forums
Ensure there is a JIRA issue, if appropriate, and claim it
If you are doing work that will be part of the shared Bahmni product (i.e. not an implementation-specific customization) then you need to ensure there is a JIRA issue to track your work.
See Issue Tracker (JIRA). (If you're a new developer who doesn't have an account yet you will need to ask someone else to create the ticket for you.)
Write tests and code
continue to update people on the chat and/or discussion forums as you do the work: this avoids someone having to review a large/major change without prior warning and it lets people suggest improvements as you're doing your work.