The road from Arusha to the Lodoare Entrance Gate is now paved and takes just more than 2 hours; the crater can be reached in a sedan, but beyond the crater (to Serengeti) you will need a 4X4 vehicle. Traveling to Ngorongoro by vehicle is recommended, as it will give you ample opportunity to shop for crafts along the way and allows you to set your own pace, taking whatever detours you deem worthy (note that Karatu, the nearest town to Ngorongoro Conservation Area, has a 24-hour ATM on the main road; it may not be operational, so don't rely on this, but it will be the last source of cash till Lake Victoria). By contrast, the road from the crater to the Serengeti is quite possibly the worst in Africa -- no one drives on the demarcated road, and even the tracks that have been made on either side of this are corrugated hell.
Aside from the atrocious state of the roads between the crater to the Serengeti, the conservation area is professionally run, with an excellent website, www.ngorongorocrater.org (or the slightly less user-friendly www.ngorongoro-crater-africa.org; in the unlikely event this does not answer all your queries, call tel. 027/253-7046 or 027/253-7019, or write to firstname.lastname@example.org).
Daily entry permit to NCA costs $50 per person ($10 for children 5-16, 4 and under free) plus an additional daily vehicle permit fee ($40-$300, depending on weight). To visit the crater, you will need to fork out an additional $200 per vehicle.
Note that NCA wardens will not allow vehicles into the crater before 6:30am, and all vehicles need to be out by 6pm (latest descent is at 4pm). As is the case at Lake Manyara, an early start is well rewarded. Most visitors depart after breakfast and take a packed lunch; to miss the crowds, ask your lodge to pack a breakfast, leave early enough to start your descent through the mists at 6:30am, and return for a late lunch.
Aside from the wildlife in the crater, you may wish to visit a Maasai cultural boma; the entrance fee is hefty (around $100 per person), and some report that the Maasai can be rather pushy about buying souvenirs. As fascinating as the Maasai culture is, I have always found the "meet the tribe" routine a little fake and awkward, but if you wish to experience it firsthand, there are four good options. The first two are conveniently situated on the road to Serengeti (but, as a result, are the most tourist savvy): Kiloki Senyati Cultural Boma is 7km (4 1/4 miles) southwest of the Olduvai Gorge Information Center, while Loonguku Cultural Boma is 10km (6 1/4 miles) before the turn-off to Olduvai Gorge. Irkeepusi Cultural Boma is 2km (1 1/4 miles) northeast of the Lemala mini gate, on the main road to Empakaai, and Seneto Cultural Boma is just west of the Seneto Gate, within the Malanja Depression. There are two more craters you may wish to visit, both of them rarely included in itineraries and, therefore, wonderfully solitary experiences. Olmoti Crater is about an hour's drive from Ngorongoro Crater and must then be approached on foot, but the more spectacular is Empakaai Crater, a 2-hour drive on rough roads (4X4 only). This crater floor lies 300m (984 ft.) below the forested rim and is almost 6km (3 3/4 miles) across, half of it (depending on rain) a soda lake; even more stunning than the crater itself are the views of Ol Doinyo L'Engai.
Blowing Hot & Cold -- Between 1,580 and 3,600m (5,184-11,811 ft.) above sea level, temperatures on the Ngorongoro plateau can get decidedly chilly, particularly at night and in the mornings. It's best to dress in layers, as temperatures can rise to T-shirt level by noon.
We're People, Not Wildlife -- While traveling the Northern Circuit it is impossible not to fill your camera with images of the most awesome landscapes and wildlife encounters, but resist the urge to take photographs of people on the roadside (the Maasai, in particular) without first asking permission. Permission may not be granted, or will be for a fee, sometimes as high as $10 per person, in which case you may refuse with good grace. However, to take a photograph without permission is considered the height of rudeness and is asking for trouble.