If you want to make it work only on Joomla 3.x then read carefully the backward compatibility issues docu.
As I migrated my extensions I had basically to do:
- Search for JView and replace it with JViewLegacy in the files
- Convert your view files to support bootstrap in front and back
- Search for DS and replace it with DIRECTORY_SEPARATOR (or do it lazy and define DS by yourself)
And the rest of the time I spent hunting for little bugs.
If you want to make it work on both versions then I suggest to have a look on FOF, which makes the hard work for you.