They already started the right way.
MediaGo is actually rather good (despite the horrible name), and it's WAY better than iTunes. They have also long since abandoned ATRAC and DRM, with all their products accepting MP3, WMA/AAC and some supporting FLAC (more FLAC please!). Their Walkman range is the best sounding devices on the market bar-none, and they do not rely on special software to use (you can just copy music to them using explorer).
I see 3 things Sony need to do to fully get back on track.
1/ Support FLAC across the range. (or at least on their quality focused kit like the PS3 and Walkman)
2/ Move Walkman to Android and get their streaming and store app on the Marketplace for all (not just Sony products) to use.
3/ Integrate their online service with PSP/PS3 their Bravia range in addition to the Android stuff.
4/ Ensure content bought once can be played on ANY of the devices above.