Marketing: However recognisable Google is as a brand, to enter the cutthroat smartphone space without a full-on ad blitz was a suicide mission. There were was advertising on the home page - a rarity, but not a buzz generator - but otherwise the majority of consumers didn't know what a Nexus One was, or if they did, why it was better or different. Next time out, be willing to spend some money to make some sales.
Sell It In Stores: By not offering the Nexus One in storefronts, Google's asking people to pay them $US180 for a product they've never even held. That's a lot of blind faith, especially considering Google had no mobile hardware track record. They're also missing a huge sales opportunity from folks who come in at the end of their contract looking to upgrade. Put the Nexus Two in a place where people can see it, try it, and buy it - and have your retail partners actively talking them into it - and it'll move a lot more units.
Improve Customer Support: Google didn't provide direct customer support for the Nexus One until a month after its launch, on the heels of numerous complaints. But even that's limited to order status: Nexus One owners still need to call HTC for hardware support and T-Mobile for billing support. That's three different customer service points of reference for customers, which is two too many. If you're going to sell a Google phone, make sure people can turn to Google for help when it doesn't work.
Get a Better Carrier: T-Mobile's network is a big ol' strugglebear. It's in the habit of losing customers, not gaining them. So the problem is two-fold: you've got a relatively small group of T-Mobile customers who could buy the Nexus One on contract, and a service provider that no one would go out of their way to join. There's always the unlocked version, but paying $US530 for a phone - even a really, really good one - just doesn't make sense given the other options out there. Put the Nexus Two on Verizon, or even Sprint or AT&T. See how well it does then.
There it is, Google: your four-step plan to cellular success. The most surprising thing of all might be that you didn't do any of it in the first place.