Hi,
From desktop support you might move on to Server/Back-end support after some time.
Windows Server 2012 might be a good starting point, have a look at the MCSA Server 2012 certification:
http://www.microsoft.com/learning/en/us/mcsa-windows-server-certification.aspx#fbid=nTemxTEp9eN
If you have done a training on XenDesktop 5 administration you might also consider to achieve the certification for this.
Getting work experience is Always difficult, if your current employer also supports Windows Server back-ends or Citrix environments then you should discuss with them if there are
any possibilities to learn on the job or have a more experienced support engineer assist you in learning Citrix or Windows Server platforms on the job.
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MCSE:Server Infrastructure, MCSE:Desktop Infrastructure, MCSA Server 2012, Citrix CCIA & CCEE, Cisco CCNA, VMware VCP 3/4/5 Blog: http://www.citrix-guru.com and http://www.rds-support.eu Twitter: @dnyvandam