This is a tough exam but managed to squeeze through a pass, was touch and go through the exam as there were quite a few tough questions, wasn't sure if I had done enough to pass but thankfully all my hours and hours of study paid off, took 6mths but I am now MSCA Windows 8.1!!!
My studies consisted of:-
Transender practice exams (Loads harder than both exams)
MS Offical Exam Ref - 70-688 (Used mostly as a guideline to drill further into each objective which was done on Technet)
Loads of on the bench practice
MS Virtual Academy & MS Virtual labs
The hardest hurdle I had was the Intune material, I came into these exams when Intune had a huge face lift and indeed re-structure, all meant study material was obsolete and had to do a lot of looking around for correct versions of stuff, if I am honest I thought I was wholly unprepared for this side of the exam, but thankfully the bits I did focus paid off.
Need to focus on the family a little now as I think they have forgotten what I look like

Hope the above helps even thou this exam retires this November.
PS: Big thanks to Techexams forums, weird as it sounds it helped me keep focused and not to give up!