Network administrator tools/responsibilities

i have taken over as the company's network administrator i was wondering if anyone could provide some insight into what tools are available out there as well as what good practices i can put into effect.
i will be responsible for the VOIP and Routers + switches.
some useful commands for trouble shooting, reading material about administration of routers, switches and call manager if possible.

thanks in advance.
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The first thing I do when starting working with a new network is build a management and monitoring box with useful tools such as Nagios, an SNMP server, NTop, etc.Get all the logs in the same place to a central syslog server is also a good idea for easy analysis. Readily accessible tools such as tcpdump and iperf are always useful as well. Configure Nagios alerts to email you or better yet configure an email to sms gateway so you are aware of problems as they happen.  

This is pretty general advice though...what OS's and equipment are you supporting?  If you can provide a little more info - can give you more specific information
First i would make sure you have access to all the devices and backup all the configs...goes without saying
Then i would get on Visio or something similar and diagram the entire network layout
Then just like Rochy said get some central monitoring going snmp, syslog, etc.
I would also setup some out of band management on devices like edge routers so if the device is down you can dial in and access it

a good general network admin book i reccomend is called Network Warrior, here is the Amazon link
its pretty cisco focused but covers a lot of different things you need to know about managing a network. It's not just about how to setup trunks or configure EIGRP but also good suggestions about things a network admin should do in his job (a few of which i mentioned)
I had a similar question that I posted earlier. You might find some awesome tools on this thread:

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As akalbfell suggests, Network Warrior is a great's quite cisco orientated, but that's not a bad thing, although a reasonable understanding of network protocols is assumed...

No matter how small the network is, you will also benefit from asset management and possibly a ticketing system.  I use GLPI and OCS Inventory (linux based but easy installs)....
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