The problem with ubuntu (and any new mobile OS in the past few years) is that they do not innovate, they simply copy and add a few gimmicks.
Developer tools need to be available WAY before the launch. They need to be free. Pay developers for startup apps. Make an office suit, a few games, etc. and make them freely available for everyone. Make them run android binaries (last I've heard, the dalvik code is open source). See those cloud services others charge for? Make them free.
Let your hardware partners go crazy. Don't impose guidelines, just make sure all binaries will run. The rest, leave it to them so they are not all clones of one another (like windows phones).
Be ready to spend a few millions without return of investment.
And above all, don't try to keep your competition out, invite them in. Google develops for iOS and with that they give out a good company image to iOS users. Maybe those that love the new Maps app will want to get it on android without the limitations. Having a full set of google services would be a plus.