Hi Fabiano,
 
The best way is to start by contributing patches for open issues or for customizations that you have already implemented and believe that it will be useful to others.  You can also use this mailing list to discuss any features that you are thinking of implementing and get feedback.
On Fri, Aug 13, 2010 at 8:28 AM, Fabiano <phabbianno@gmail.com> wrote:
How do I contribute to the development of talent in Mantis with my
php. Already customized here at my company and would like to suggest
improvements