Many structures in SimCity create a radius zone when you place them, this radiant is shown as either a circle around the structure or dots along the roads depending on the kind of structure you're placing. Parks and plazas create a radius zone, as do schools and police. Each of these structures provides an increase to land value for properties within that area.
The size of the area that is within the radius depends on the structure being placed, parks and plazas will affect a smaller area in comparison to police stations or fire stations. Placing multiple parks or plazas with their radius zones overlapping will stack, providing a greater increase in value.
Any specialisation you choose for your city will also have an affect on land value, for example specialising in Casinos will increase the value of commercial buildings in its vicinity.
Ensuring that you keep the streets of your city clean will provide you with a boost to land value, whilst letting them get backed up or not dealing with sewage will have a negative effect on your land value.
Abandoned buildings will also have a negative effect on the land value of nearby buildings, and have an increased chance of catching fire. Keeping abandoned buildings around over the long term will drive down land value for the surrounding area and it is usually recommended that once the building goes 'dark'. It is better to bulldoze that building to prevent it from causing damage to the value of the surrounding buildings.