The most convenient, and safest way to get around Hanoi is by Taxi. They are plentifull and pretty cheap. Depending on the taxi company, a trip within the city center shouldn't cost you more than a dollar or two.
Personally, I get around on motorbike, but if you don't know the city, and keeping in mind that traffic is absolutely mad, this might not be the best option for a short-term visitor.
Bicycles can be rented, but that is probably even more dangerous than a motorbike, and only really advisable within the Old Quarter.
Forget cyclos, the cyclo guys are a pain in the neck, and most roads these days are banned for cyclos. Again, this might only be an option for the Old Quarter.
Noibai Taxi very Safe and Helpful, driver was very co operative he helped in my luggage . Would recommend to others to use this taxi service.
When you arrive at Noi Bai Airport, a convenient way to get to Hanoi town is to hire a taxi - it's USD10/- per taxi. Maximum passengers is 4 adults.
If you are quoted a higher price, bargain for it.