Reporting bugs is a great way to help make Epiphany a better product. Very often problems are not fixed just because they are not known.
Translating Epiphany in your language will help to make it accessible to everyone.
You can submit patches on the Epiphany mailing list or in bugzilla. In the latter case remember to add the PATCH keyword to the bug, to bring it to the mantainer attention.
Planning for the next Epiphany releases takes place in the Epiphany Wiki.