After getting CCNA certification how to Improve your Networking Skills, system admin skills?

Although you mean to say system administration along with network administration both are totally different streams. In system administration you have sub domains like ms system administrator, Unix administration, anti virus and desktop related. However in network you have network admin, network operations, routing switching, lab cabling, fiber optics, firewall rules, network security and other. Even ms exchange comes under system administrator . so first choose what you want to learn and refer simulations, try to get some projects, also it's very important to know the basics like different types of routing technologies, emerging concepts like virtualisation in networking, etc.