Campaign in Latest
Publish the campaigns to My Feed in Studio (appears under Latest in the member experience). As long as only a limited amount of content is published to My Feed and your community does not leverage Auto-Follow too much, publishing to My Feed will make the content among the first things that new users see after registration.
Include images to and text to encourage users to open the campaigns.
Campaign with Acknowledgement Requirement
Create an article post and enable a campaign to target users that are already in your community. Set the campaign with the Acknowledge feature and a high priority. This solution is not recommended for communities that are just launching, as users that join the community after the campaign has started running will not be pulled into the campaign. Acknowledgment would work best for an established community that has recently updated the Terms of Service - a way to say "check this out". A high-priority campaign will automatically follow up with users that have not yet acknowledged the post.
Tracking Outside Studio