Via Co-Creative Recipes:
"OpenStreetMap is only as good as the contributions of the people who edit it. To encourage and help people to edit, OpenStreetMap enthusiasts can run Mapping Parties. Mapping Parties come in many flavours, but generally the idea is to get together to do some mapping, socialise, and chat about making a free map of the world!
It is a convivial community event, open to all, and although some folks will be mapping experts, newcomers are always welcome. It’s great way to find out more about the project, and if you’ve never gathered map data for OpenStreetMap before, it’s a great way to learn how. Some mapping parties are very specifically targeted as a training event for new mappers. This can even involve the organizers lending out GPS units to have a play with some gadgetry (although GPS is not required for OpenStreetMap mapping)
The schedule of a mapping party can take several forms, for example a simple mapping party can just involve going to a nominated pub after doing some mapping, but typically a larger event will involve meeting beforehand to discuss the plan and to team people up. Afterwards, the event may involve use of laptops/computers with internet, to actually input the data gathered that day, or it may not (For a simpler mapping party, participants take their data and input it later at their leisure)
For effective training of beginners it’s a good idea to have at least one laptop, to demonstrate editing. Be prepared to use JOSM’s offline capabilities (download and save a .osm file beforehand) in case you have no internet. If GPSs are involved it’s a good idea to take the data off the device by way of demonstration, and because this is a tricky part which beginners can fail to do when they get home. This way you can upload their file for them.
After the mapping is finished, the participants share food and drinks, and enjoy themselves. It’s a party, after all! Indeed mapping is not compulsory at a mapping party. Sometimes it’s all about the party!" (http://www.co-creative-recipes.cc/recipes/mapping-parties/)