Agile Methodologies: Iterations iterations iterations... it's always about being flexible!
Test Driven Development:
Writing tests always first enforces better and cleaner code.
Version Control: Distributed VCS (Git, Mercurial), centralized VCS (SVN)... You name it.
Developing for Mobile: Great understanding of mobile development - writing for limited resources (Memory, Computing Power, Energy)
Other programming languages: Java (and that includes Android too!), C, C++, SQL
Clean Code Evangelist: Keep It Simple, Stupid!