Okay first of all you need a foundation certification - stick to vendor certifications (Those provided by vendors in the IT industry such as Cisco and Microsoft.
Get these first (only if you don't have foundation knowledge):
- CompTIA A+
- CompTIA Network+
- ITIL Foundation (Information Technology Infrastructure Library)
- CompTIA Strata Green IT
- CompTIA Security+
But if you have foundation knowledge you then need to choose from the following:
1) Database Administrator
You support database nodes and specilise in the security and management of stored data. 99% of specialised database admins work in financial institutes such as banks and insurance companies. I've personally managed the databases at QBE as a contractor in the UK. I thought I'd be doing a lot of work until I found out they have over 100 database specialists in their India office!
2) Linux Administrator
Much more complex, much more rewarding, much more skillful and much better paid! Dedicated to Linux networks ofcourse. Focus on Red Hat certifications and practise by playing around with Linux distributions. I'd recommend you train VERY hard on CentOS, RedHat and Ubuntu. Linux admins (good ones) can easily land a job earning £60,000 - £80,000. I have three friends working at the BBC who earn a similar salary.
3) Windows Network Administrator
This one is simple - but that's caused the industry to become saturated. Get yourself a foundation networking certification such as the CompTIA Network+ if you haven't already and then focus on the MCSA: Windows 7 (If you're going to administer Windows networks you WILL be using Windows desktop). Once you're clear there progress and get a MCSA Windows Server 2012 AND Windows Server 2008 (Some companies won't upgrade for another 8 years!). Then get your MCSE: Server Infrastructure. This is enough to get yourself a career earning £26,000 to £38,000; dependent on exxperience and skill. A serious goal you could aim for is the MCSM: Directory Services. This is enough to land someone in a Third Line Support role. You'll also find yourself treated like a god (people will WANT to employ you) if you're confident in powerShell.
There are many others but I listed the key ones as I don't have all year :)
Hope it helped!
Source: This is my beloved career and hobby. I specialise in Linux but can also kick the ass out of a windows network. I can navigate AD and Exchange with my eyes closed.