As suggested by weinstein5 start off with the blueprint, there are some study guides avilable online which can be used as referece for surdy material
Below linke you will find some good collection of study guides
http://thesaffageek.co.uk/vsphere-5-study-resources/vcap5-dca-dcd/
In addition you can attend
VMware vSphere: Optimize and Scale [V5.1]
training which will help to prepare for VCAP-DCA exam
