The town is well-connected to the north and south by bus. The AXA bus line provides quite civilized transport at a reasonable price. There are also cheaper, rickety buses available, as well as the usual minibuses which hold up to 20 people - scary but cheap.
If coming from Mbeya, Tanzania be careful of well established scam artists selling fake bus tickets. One of the scam artists even has an office in the main transit area in Mbeya. He also has professional looking lists of prices, services, etc. He may even use a cell phone to check availability of seats for you. As of April 2013 there were no buses running from Mbeya to Mzuzu or any other town on the Malawi border.
Instead, take a minibus from Mbeya to the border town of Songwe (the minibus terminates at Kyela, slightly further down the road). If a direct from Mbeya to Kyela is not available, make a change at Tukuyu. This first leg from Mbeya to the border costs about Tsh5,000 and takes 3hr30min. From the minibus stop, it is a 15min walk (or a TSh1,000 motorcycle ride) to Tanzanian immigration, and another 10min across the bridge to Malawi immigration. A currency exchange office sits on the Tanzanian side of the bridge, in a yellow building. Once past customs, take a shared taxi (K700 a person, 50min) towards the transit center of Karonga. Minibuses leave from Karonga to Mzuzu once full (4hr30min, M2,000-2,500), but waiting for passengers could take a few hours. Leaving Mbeya at 08:00 will mean an arrival in Mzuzu around 17:00-19:00, depending on the wait at Karonga. Note that Malawi is an hour behind Tanzania.
Swiftair operates scheduled flights from Lilongwe to Mzuzu and karonga on a twin engine, 2 crew beechcraft 1900 http://www.swiftairmalawi.com
Mzuzu is small and navigable on foot.
Other than typical African market goods, there's not a lot to buy here. It does, however, possess the most northern ATM's, good if you've just come from Tanzania or find yourself staying longer in Nkhata Bay than planned.
A-1 Restaurant - located on the street behind the main banks and groceries in a commercial strip. Certainly the best food in town with a menu focusing on Indian fare with some Chinese selections. Extensive choice of dishes that are generally quite good. Prices are fairly steep for Mzuzu, but very reasonable by western standards.
Obrigado Leisure Park - centrally placed with hideous red and yellow advertising for Celtel. Inside the fence you will find a beautiful garden with tables interspersed throughout. The food is typical Malawian restaurant fare, including nsima or rice with your choice of meats or relishes. A bit of a beer den at night, it seems.
There is also a pizzeria near the bus station on a side street serving decent thin crust pizzas cooked in a wood fired oven. It is run by an extremely entertaining couple named Paolo and Emanuelle. Next door is Paolo's trading post stocked with some western luxuries such as M&Ms and decent toilet paper.
Nkhata Bay is about an hour away by bus or pickup truck.