The Canaima National Park is one of the most beautifull regions of the World, IMnsHO.

It is composed of the northern sector, where the Lagoon of Canaima and Auyan-Tepui with Angel Falls are located, and the High-Plateau known as the Gran Sabana, which reaches a height of some 1400m above sea level, slowly falling towards the Brazilian Border.

The Lagoon of Canaima and subsequently Angel Falls are best reached by plane. There are flights either from Ciudad Bolivar, or MArgarita Island, or Caracas, at the very least, normaly small planes. The flight time from Ciudad Bolivar is approx. 1h, from Margarita 2h. If you're lucky, you get to see the Lagoon as the plane descends towards the Canaima Airport (landing strip with attached hut...). The Lagoon is a beautifull spot anytime of the year, and on a tour through it, you get the chance of walking behind a waterfall. Organised trips to the Lagoon usually include an overfly of Angel-Falls, weather permitting.

From the Lagoon, you can take a boat upriver towards Auyan-Tepui, to view Angel Falls from the ground. There are 2 variants for this trip: the most frequently offered includes an overnight in the Canaima village, with the trip to Angel Falls starting the next day around 5am. The boat trip takes approx. 4.5 h, to an island from which the walk to the mirador starts. It takes from 45min to 1.5h to walk from the landing spot to the mirador. The night is spent in a local camp, mostly sleeping in hamacs, the trip back to the Lagoon being made on the next day.

The second variant, offered, so far, only by one camp that I know of, starts on arrival day with a tour of the lagoon from which you directly start towards the base camp, one cañon before the one where Angel Falls is. It's a 2h boat-trip. Overnight stay at the camp, sleeping in hamacs. On the next day, 2.5 h boats-ride to the island for the Angel Falls walk, return to the base camp after lunch and rest. Overnight stay at the camp, again, with return to the Lagoon on the third day, in time for lunch.

Both variants take 3 days, but are well worth the trip. Best times are May/June to October/November. Avoid if possible the dry season (officially starting October, and lasting until March/April), as at that time the water level in the Churun river can get so low that the river becomes unnavigable.

The Gran Sabana is traveled mainly by car, or more precisely by Jeep. There's a "highway" running through it from north to south, leading all the way to the frontier town of Santa Elena de Uairen. Appart from that, it's dirt road.
There are many agencies offering tours through the Gran Sabana, from a drive-through, to trips up Mount Roraima, so take your pick. The waterfalls are nicer during the rainy season, of course, but the chances of getting wet are greater too, so it's up to each one to decide when best to come.
Do avoid the main local holidays (from around december 15th to around january 12th-15th) as the park is filled with venezuelans.

There's only one hotel in the whole park, since by regulation only the Pemon indians can use the resources of the park in any way. The other options are at both ends: the town known as km 88 (San Isidro, officially), and Santa Elena. Santa Elena is the nicer of the two options. If you stay there, do visit the church. It's one of the nicest in Venezuela. And take a sidetrip to La Linea, just over the Brazilian Border.
For this, make sure you are vaccinated against Yellow Fever, as you will not be allowed across otherwise.