Listen, I feel like I can speak for all of humanity when I say that we're all exhausted with the heaps of junk mail brought to us daily, but the reality is that your new construction home needs an address for deliveries, navigation and emergency services.
Many buildable lots already have addresses but some don't. If you already have a street address then you can skip steps 1 & 2.
Step 1:
Contact the Proper Local Department.
While your first instinct may be to go to USPS, they don't actually regulate street addresses, instead local jurisdictions do.
The department that handles street addresses can vary by locality but it may be the building department, zoning department or similar.
Questions to Ask:
A. Ask them how long it takes to process a new address. Since processing time can vary, you don't want to move in then have to wait two months for an address.
B. Ask what the minimum completion requirements are. Many jurisdictions will perform a site visit before assigning an address. Some may require that the house has reached a minimum level of construction (foundation or rough framing, etc) or that there is a driveway laid.
C. Ask them how to get the required forms or paperwork and what documentation is required.
Step 2:
Fill out the Paperwork
The local jurisdiction will provide you with a form and list of required documents to proceed. Fill them out and pay close attention to detail. These documents typically include the deed, mortgage paperwork, multiple forms of ID, floor plan and site plan. There may be a processing fee.
Step 3:
Register the Address with USPS
Once the local jurisdiction has finished processing your paperwork and delivered to you an official address you can't call it quits because mail won't just start coming in. You will have to go to your local USPS branch and request to fill paperwork for a new construction address with the local post master. Mail will typically start being delivered within a week.
Step 4:
Install a Mailbox & House Numbers
In the US, mailboxes are regulated but there are many different variations that can be found.
Regulations on driveway mailboxes and wall mounted mailboxes can be found here.
House numbers are regulated by the local jurisdiction so you'll need to contact them for their exact specification. Usually regulations include height, elevation, contrast/color and visibility.
Step 5:
Fill for Change of Address and Update all of your Personal/Financial Account addresses.
The USPS Change of Address website can be found here. It usually takes a few days to process.