Guerrero Negro is a city in Baja California Sur, on the edge of the Vizcaino Desert just south of the state border about halfway down the peninsula. It is best known for the whale watching, although its primary industry is salt.
The easiest and more comfortable way is by small plane: there is a company that flies from Ensenada to Guerrero Negro on Monday, Wendesday and Thursday at 11:30, it makes a stop at Isla de Cedros. The company is Aeroservicios Guerrero, and the phone number is +52 (615) 157 01 37.
To get to Ensenada you may fly to San Diego and take the bus at the station that is just across the border in Tijuana. There is also a bus that leaves from the airport in Tijuana each hour from 8:30 am and it arrives in Ensenada two hours later. You can also fly to Los Cabos or Loreto via commercial airliner from the US.
Another way to get to Guerrero Negro is to rent a car in Tijuana and make the 12 hour drive. It is a long drive but it is worth the trip, and it is cheaper if you are two or more people.
Guerrero Negro is a stop from points south and north, Autotransportes de la Baja California  serves Guerrero Negro. Service should be regular, but inquire ahead of time.
Tijuana Central Station to Guerrero Negro leaves at 12:15, 16:00 and 18:00 hrs and it takes about 12 hours to get to Guerrero. La Paz to Guerrero Negro (12 hours from La Paz) leaves at 10:00 am, 4:00 pm and 11:00 pm, from Loreto the jaunt is at least 4 hours shorter.
The lagunary complex of Ojo de Liebre has been recognized as a wetland of international importance by the Ramsar Convention and as a Hemispheric Importance Site for shore birds conservation so bird watching is a must.
The sand dunes around the Guerrero Negro Lagoon can also be visited.
There are guided visits to the largest open salt company and to the rock paintings at San Francisco and Santa Marta Sierras as well as to lesser known paintings of Mesa del Carmen, north from Guerrero Negro.
Guerrero Negro is the place with the highest concentration of grey whales in the world. The whale watching tours in this area are almost mandatory. Also, visit the largest salt works in the world, do some bird watching in winter, see giant sand dunes and one of the largest concentrations of Osprey's in the world (they hatch by the end of February). Malarrimo Restaurant has a little museum on the bar side with a nice collection of flotsam recovered from Malarrimo Beach. There are sand-blasted bottles, fishing floats from japan, pieces of ships, wooden oars, round army containers about three feet long and eight inches in diameter, lots of construction helmets, and a wooden ships wheel, etc.
Tours leave at 8am and 11am and cost US$50 or MX$650. (as of Feb 2012)
Eat at Mario's, the biggest palapa in Baja California, with a very unique ambience and very nice local sea food specialties. 
Realize that all accommodations are very basic.
Geting out is not easy as it is a wonderful place to spend some days, any how, the ways out are the same to getting in.