If you want to publish a version of your module under a tag other than latest (which is what is used by default), then simply include the --tag option when publishing with the name of the tag you wish to use.
For example if you want to publish with the tag "beta" you would type:
npm publish --tag beta
The version you have just published will be registered under the beta tag rather than the latest tag, and will not be installed when someone attempts to install your package with the npm install
You can install different tagged versions using the npm install --tag
npm install forerunnerdb --tag dev