Like any other services, they need to promote the services and let people know what they are trying to achieve.
They need to inform people about the project, not only to developers but also to the public.
Governments spend significant capital to collect data, make websites, and to maintain the service. Once they put foot in it, they cannot just let it go and expect someone to use it. It is only a start; they need to let people know, involve in communities, improve the services, and provide the data that people want.
It may be good enough for government officials to say, "I opened the data, and we are transparent. Now anyone can access the data."
However, real benefits from providing the data to public can be seen only when governments put significant efforts in after the launch.
Nat Torkington, who has involved in two open data projects, Open New Zealand and data.govt.nz, suggests for those starting or involved in open data projects.
First, figure out what you want the world to look like and why. It might be a lack of corruption, it might be a better society for citizens, it might be economic gain. Whatever your goal, you'll be better able to decide what to work on and learn from your experiences if you know what you're trying to accomplish. Second, build your project around users. In my time working with the politicians and civil servants, I've realised that success breeds success: the best way to convince them to open data is to show an open data project that's useful to real people. Not a catalogue or similar tool aimed at insiders, but something that's making citizens, voters, constituents happy. Then they'll get it.
Open data phenomena has moved into the next stage; many governments have opened data and start realizing its value of it, now they need to improve their services to make these actually useful.