For 11+ practice I would highly recommend Bond books (including the various test paper collections and the parents' guide) and the NFER packs (papers).  These have been invaluable to me and my students.  They love them, they are set out clearly and are easy to read.  

If a child practises these papers at home, they should firstly start off by sitting the paper at their own pace then move on to timed papers.  This will give you a guide to how they will handle working to a limit.  

With the 11+ plus it is recommended that you give the child plenty of time to prepare and practice, that its not a hurried process and that ultimately they feel confident in what they are doing.

Good luck!