You can get to Sapa on train or on bus from Hanoi. The train is more convenient. There is even a luxury train departing every evening to Lao Cai from Hanoi's main station. If you are traveling in a normal train, buy the soft sleeper tickets.
You get to Lao Cai at first time in the morning -- mostly before dawn. From there you get on a minibus, and in a couple of hours you are in Sapa. The views from the road are awesome.
Most of the times, you will have to wait till 12 to check into your hotel. Meanwhile you can go for a walk in the town center, have a good breakfast, and relax in one of the terraces. Once your room is ready, you can have a nap, take a shower and eat something. In the afternoon, you can visit the town in the valley down Sapa.