Hello Catalin,
Some things you could do now:
1. Clone the trunk repository and build Inkscape
1.1. Use ccache to speed things up for repeated building of Inkscape
2. Have a look at random locations in the source code to get a high level understanding how things fit together.
3. Bugs/Patches:
3.1 Submit a patch for any bugs you fix from the bug tracker. You'll need a Launchpad account.
3.2 Refactor an existing bit of code by making it faster/better/cleaner/more-readable and then submit your patch. For example, I changed the usage of a g_hash_table to std::map. I think there are still some more usages of a g_hash_table in the codebase, so changing it would be a quick first patch.
4. Familiarity with libsigc++, gtkmm, bzr and the C++ STL will be very useful.
5. Once you clone the repo, generate the Doxygen documentation. I found this useful to visualise the heirarchy of the classes, and also as a reference to look up what methods I could use, etc.
@Everyone: What have I missed covering?
Samuel