Develop a NAC Policy
The first step in implementing effective NAC is to develop a policy that outlines the rules and procedures for granting network access. This policy should be tailored to your organization’s specific needs and take into account factors such as user roles, devices, and applications. It should also include clear guidelines on how to enforce the policy, such as the use of firewalls and intrusion detection systems.

Identify and Authenticate Users
To ensure that only authorized users have access to your network, it is important to implement strong authentication methods. This can include usernames and passwords, two-factor authentication, or biometric authentication. In addition, it is important to regularly review and update user access privileges to ensure that they align with current job responsibilities.

Segment Your Network
Segmenting your network can help to limit the spread of malware and other security threats. By dividing your network into smaller subnets, you can control which users and devices have access to different areas of the network. This can help to prevent lateral movement by attackers and limit the impact of any security breaches.

Monitor and Enforce NAC Policies
Monitoring and enforcing your NAC policies is critical to maintaining the security of your network. This can include monitoring user activity, network traffic, and device usage. By analyzing this data, you can identify any suspicious activity and take appropriate action to mitigate any potential threats.

Regularly Update Your NAC Solution
Network security threats are constantly evolving, which means that your NAC solution needs to be updated regularly to stay effective. This can include updating software and firmware, adding new security features, and patching any vulnerabilities that are identified. Regular testing and validation of your NAC solution can help to ensure that it is functioning as intended and providing adequate protection for your network.

In conclusion, implementing effective network access control is critical to maintaining the security of your organization’s network. By following these best practices, you can help to prevent unauthorized access, limit the spread of malware, and protect sensitive data. Remember to regularly review and update your NAC policies and solutions to stay ahead of the evolving threat landscape.

SANS Institute has a great paper on the above subject.