How you can get securer in network?

through adding a network IPS/ IDS, HIPS & NIPS

1- First you have to define the perimeter of your network; External inputs and outputs for WAN or to Internet.

2- Isolate critical network zones (with Firewalls)

3- Define your DMZ (If you have serves with externals communications)

4- Manage access rules for your users (Firewalls rules (IP adresses and Ports))

5- Use IPS (or IDS) for externals link

that's all

Some main considerations:

1. The company should have a public security policy containing "Computer Network Security" as part of it
2. Apply security rules related to each node in your network as far as you can do, example if it is a server then only open requiredd ports for connection made to and from this server
3. Employees should have a public awarnes about public risks, example never get a portable starge to the work place for many considerations1 of them it could be infected with a virus
4. There must be an IDS installed in the network
5. Any traffic going out to or from the internet must be filtered

Hope this was useful for you