The first step towards successful discovery planning is to identify the list of candidate subnet(s) having the target endpoints. This will be important in planning the virtual appliance deployment and creating scan jobs.
In the case of sparsely populated subnets, it is recommended that you list down the specific target IPs and IP ranges having the target devices. This could help in creating highly efficient scan jobs with specific target endpoints(IPs and IP ranges).
Once you have identified the target subnets, and IPs, it is time for Step 2 - Plan Your Virtual Appliance Deployment Strategy.